Methods, devices, and systems for measuring physical properties of fluid

ABSTRACT

Disclosed herein are devices for measuring, at one or more time points, one or more properties or changes in properties of a fluid sample. The devices may comprise a chamber defining an internal volume of the device suitable for receiving and retaining the fluid sample; a plurality of layers, the plurality comprising at least a first layer below the chamber, at least a second layer above the chamber, and a substrate layer between the first and second layers, wherein: the substrate layer is linked to at least one suspended element located within the chamber; the suspended element is linked to the substrate layer by at least two compliant structures located within the chamber; and the suspended element is configured to oscillate upon application of an actuating signal to at least one electrically conductive path, which runs across at least two of the compliant structures and the suspended element. Related methods and uses are also disclosed.

This application is a division of U.S. application Ser. No. 13/742,244,filed on Jan. 15, 2013, entitled, “METHODS, DEVICES, AND SYSTEMS FORMEASURING PHYSICAL PROPERTIES OF FLUID”, which claims the benefit ofU.S. Provisional Patent Application No. 61/587,020, filed on Jan. 16,2012, entitled, “METHODS, DEVICES, AND SYSTEMS FOR MEASURING PHYSICALPROPERTIES OF FLUID”, which is incorporated herein by reference.

The present invention relates to methods, devices, and systems formeasuring physical properties of fluid, e.g., viscosity of a fluidsample, viscosity of a bulk phase of a fluid sample, viscosity of acontinuous phase of a fluid sample, viscoelasticity of a fluid sample,density of a fluid sample, plasma viscosity of a blood sample, wholeblood viscosity of a blood sample, viscoelasticity of a blood sample, ablood clotting time of a blood sample, a hematocrit of a blood sample,and a concentration of anticoagulant in a blood sample.

Whole blood viscosity (WBV), a global measure of the intrinsicresistance of bulk blood to flow in vessels, is determined by theinteraction between blood cell rheology, plasma viscosity (PV) andhematocrit, and may be considered a marker of circulatory function. Itsmajor determinants are the volume fraction of red blood cells(Hematocrit or Hct), plasma viscosity (determined mainly by plasmafibrinogen, other biologically reactant globulins, and lipoproteins),red cell deformation (under high flow/shear conditions) and red cellaggregation leading to clotting/coagulation (under low flow/shearconditions) [1, 2]. It has been shown that increasing levels of bloodviscosity within the general population may promote cardiovascularevents through its potential rheological effects on atherogenesis,thrombogenesis, or ischemia distal to atherothrombotic stenoses orocclusions [1, 3]. Epidemiological studies have associated high bloodviscosity with conventional risk factors such as the male gender,cigarette smoking, blood pressure, and plasma lipid/lipoproteins [2, 4].A study of a random population of 1592 men and women, followed over amean of 5 years, showed mean blood viscosity, after adjustment for ageand sex, was higher in patients experiencing ischemic heart attacks andstrokes than those who did not [5]. After correction for diastolic bloodpressure, LDL cholesterol and smoking, the link between blood viscosity(and hematocrit-corrected blood viscosity) was significant only forstroke (p<0.05). A recent prospective study of 331 middle-agedhypertensive men (followed for an average of 4.8 years) revealed thatthe top tertile diastolic blood viscosity patients had increased risk ofcardiovascular events [6]. Also, there is a strong correlation betweenthe incidence of type-2 diabetes with WBV, and both the prediction ofplasma hyperviscosity syndrome and the prognosis of sickle cell diseasewith plasma viscosity.

Blood is a non-Newtonian fluid, i.e., the viscosity of blood isdependent on the velocity of blood through vessels (more specifically,blood's shear rate). At high velocities of blood, the disc-shaped redblood cells orient in the direction of the flow and the viscosity islower. For extremely low shear rates red blood cell aggregation mayoccur, thus increasing viscosity to very high values. It has also beensuggested and demonstrated that a minimum shear stress (yield stress,τ_(y)) is required before the blood will start to flow. To measure theviscosity of a sample, modern viscometers generally measure the rate offluid flow at a specified force or, conversely, the amount of forcerequired to achieve a predefined rate of flow. It does not matter whichmethod is used for plasma viscosity measurement due to its Newtonianfluid properties. The rate of flow (proportional to shear rate) ideallyshould be precisely controlled and specified when measuring whole bloodviscosity so as to foster standardization of measurement. Viscometerscommonly derive the viscosity of a fluid by measuring the force requiredto achieve the specified shear rate (Wells-Brookfield, cone-plate typeviscometer) [7]. Conventional laboratory viscometers are often notconducive for portable and online measurement of viscosity due to theircost, space requirements, and other pre-conditions, e.g., vibration-freemounting. Also, sample taking for such devices often involves manuallabor and tends to be time-consuming and error-prone.

Vibration-damping based sensors can be used for fluid propertymeasurement. The vibration based sensors when exposed to a fluid inducean acoustic vibration field in the medium, which results in aviscosity-modified damping or flow that can be measured electronically,optically, etc. When the vibration of the sensors corresponds to aresonance oscillation of the sensor, the damping of the oscillation canbe measured using the quality factor of the resonance, the resonancefrequency, and/or the resonant motion amplitude, among other variables.Examples of such sensors include microacoustic sensors like quartzthickness shear mode resonators (TSM) [10] and surface acoustic wave(SAW) devices which have been successfully used as alternatives totraditional viscometers [11]. These devices generally measure viscosityat relatively high frequencies and small vibration amplitudes, which canlead to significant disadvantages. Since the penetration depth(δ_(s)=√{square root over (η/pπf)}) of the acoustic field excited bythese sensors is small (when high frequencies are used), only a thinfilm of liquid close to the device is probed. Thus for non-Newtonianfluids or fluids containing discrete components/additives, the resultsmay not be directly comparable to results from conventional viscometers.

In some embodiments, the present invention provides an acousticvibrating sensor that can generate for relatively greater vibrationamplitudes and acoustic field penetration depths in fluids, which inturn can lead to a higher sensitivity and larger breadth of measurementof fluid properties. In some embodiments, the vibrating element is suchthat at least two acoustic fields corresponding to two differentpenetration depths can be induced in the fluid medium, and consequentlydifferent physical properties of the fluid can be measured using the twoacoustic fields. For example, by using two penetration depths that aregreater than and smaller than the size of discrete components/additivesin the fluid, the viscosity of the continuous phase and the bulk phase(which reflects contribution from discrete components/additives) can beaccurately determined in the same sample, without need for separatingthe discrete components/additives. Also, by varying the vibration modeof the sensor in a device according to some embodiments, the density ofthe fluid can also be precisely measured, which in turn may be used toquantify the concentration of any discrete components/additives. Thissensor could be found useful in a wide variety of fluid propertymeasurement applications, e.g., measurement of properties of foods,beverages, paints, and inks, as well as biological fluids in vivo and invitro.

In some embodiments, methods and devices according to the inventionprovide advantages for the measurement of whole blood viscosity, whichis highly dependent on the viscosity of its continuous phase, i.e.,plasma, and the concentration of discrete components such as red bloodcells.

Some embodiments of the invention provide sensors that enable thesimultaneous and rapid measurement of whole blood and plasma viscositieson the same blood sample and/or that can be configured to measure thedensity of blood which can be used to determine the hematocrit, becauseof the density being linearly related to the hematocrit by the simplerelationship p=1.026+0.067 Hct gm/cc [12]. Since whole blood viscosityis highly dependent on the plasma viscosity and hematocrit, in order tocompare/group the blood viscosity of different individuals it may beadvisable to standardize the blood viscosity to a fixed hematocrit (0.45is generally used). In most of the studies whole blood viscosity wasstandardized (or corrected) to a standard hematocrit of 45% by theformula of Matrai et al. [8]—

$\left( \frac{\eta_{{WBV} - 0.45}}{\eta_{plasma}} \right) = \left( \frac{\eta_{{WBV} - {Hct}}}{\eta_{plasma}} \right)^{0.45/{Hct}}$

where η_(WBV-0.45) is the corrected whole blood viscosity, η_(WBV-Hct)is the whole blood viscosity at hematocrit Hct, and η_(Plasma) is theplasma viscosity. Thus in order to estimate the standardized bloodviscosity using this approach, the hematocrit, whole blood viscosity andplasma viscosity of a sample need to be accurately determined.Currently, the measurement of blood and plasma viscosities generallyinvolves time-consuming sample processing viz. centrifugation of redblood cells to separate plasma and measure hematocrit, and measurementof viscosities using bulky instruments by trained professionals. Also,since the blood volumes available from patients are small they must beanalyzed quickly, preferably without the addition of anticoagulants. Thecurrently existing methods for clinical diagnosis and in vitro study ofblood in laboratories generally involve the addition of anti-coagulantssuch as EDTA, thus deviating from the true physiological state of blood[9]. In some embodiments, the invention provides the advantage ofperforming all three measurements viz. whole blood viscosity, plasmaviscosity and hematocrit measurement on the same blood sample withoutrequiring pre-processing of the samples, thus serving as a rapid,point-of-care diagnostics tool.

The capability of measuring the physical properties of bloodrapidly canallow for monitoring the properties as a function of time, includingreal-time monitoring of the coagulation of blood. The currently usedhemorheological tests for diagnosis and monitoring of diseases includeblood coagulation tests such as Prothrombin Time (PT), PartialThromboplastin Therapy (PTT), Activated Clotting Time (ACT) andThromboelastogram (TEG).

The above mentioned tests conducted in clinics may require large samplesof blood (3-5 ml) and the addition of anti-coagulants, often with longturn-around times of at least 1-2 days. Also, the tests generally do notdirectly measure the effect of drugs (Warfarin, Coumarin, Heparin etc.)on blood viscosity, i.e., thinning or reducing blood viscosity, butinstead measure their second order effect on blood clotting.

The currently existing hand-held point of care units used in home andanticoagulation clinics (Coaguchek™, Hemosense™ etc.), generally followthe pin-prick blood sampling and strip-based collection method as iscommonly used by blood-glucose meters, and measure blood coagulationtimes (PT/INR & PTT). Though these devices are portable and easy to use,they generally do not measure the effect of the anti-coagulation therapyon whole blood viscosity, which could indicate the real-timeeffectiveness of the drug therapy. A real-time measurement of thephysical property of the complex fluid (here, blood viscosity) may helpgive real-time feedback on the effectiveness and response time of thetreatment/therapy in a clinic allowing for tighter control. Also,monitoring viscosity as a function of time can be used in performingmultiple coagulation tests on the same blood sample (PT/INR, PTT & ACT).Such a device could in effect be used for measuring blood & plasmaviscosities and perform standardized coagulation measurements (includingbut not limited to PT/INR, PTT, ACT & TEG) for home monitoring as well,thus giving a comprehensive picture of the therapy induced changes toblood.

Thus, there is a current need for low sample volume (e.g., <5 μl,including but not limited to pin-prick blood sampling in a disposablestrip), rapid real-time measurement of rheological properties of wholeblood and plasma (viscosity and coagulation) in vitro or in vivo. Suchan instrument, together with biosensors such as, e.g., glucosemeasurement for diabetic patients, could serve as an invaluable tool forrapid diagnosis and monitoring of disease and blood function.

Accordingly, in one embodiment, the invention provides a device formeasuring, at one or more time points, one or more properties or changesin properties of a fluid sample, the device comprising: a chamberdefining an internal volume of the device suitable for receiving andretaining the fluid sample; a plurality of layers, the pluralitycomprising at least a first layer below the chamber, at least a secondlayer above the chamber, and a substrate layer between the first andsecond layers, wherein: the substrate layer is linked to at least onesuspended element which is not substantially metallic located within thechamber; the suspended element is linked to the substrate layer by atleast two compliant structures located within the chamber; and thesuspended element is configured to oscillate upon application of anactuating signal to at least one electrically conductive path, whichruns across at least two of the compliant structures and the suspendedelement.

In another embodiment, the invention provides a device for measuring, atone or more time points, one or more properties or changes in propertiesof a fluid sample the device comprising: a chamber defining an internalvolume of the device suitable for receiving and retaining the fluidsample; a plurality of layers, the plurality comprising at least a firstlayer below the chamber, at least a second layer above the chamber, anda substrate layer between the first and second layers, wherein: thesubstrate layer is linked to at least one suspended element locatedwithin the chamber; the suspended element is linked to the substratelayer by at least two compliant structures located within the chamber;the suspended element is configured to oscillate upon application of anactuating signal to at least one electrically conductive path, whichruns across at least two of the compliant structures and the suspendedelement; the suspended element and the at least two the compliantstructures are configured to have at least a first oscillation frequencyand a second oscillation frequency; oscillation at the first oscillationfrequency induces a first acoustic field in the fluid sample with afirst shear penetration depth smaller than a threshold value, whereinthe threshold value ranges from 0.5 microns to 500 microns, andoscillation at the second oscillation frequency induces a secondacoustic field in the fluid sample with a second shear penetration depthgreater than the threshold value.

In another embodiment, the invention provides A method of measuring oneor more properties or changes in properties of a fluid sample using adevice according to claim 1, the method comprising: placing the fluidsample in the chamber of the device; oscillating at least one suspendedelement of the device, wherein the oscillation causes a current orvoltage in at least one of the electrically conductive paths of thedevice; measuring the current or voltage at one or more times; and usingone or more of the measurements of the current or voltage to calculatethe one or more properties or changes in properties of the fluid sample.

In another embodiment, the invention provides a method of determiningone or more properties or changes in properties of a fluid sample at anarbitrary concentration of an analyte present in the fluid sample, themethod comprising: placing the fluid sample in a chamber comprising aphysical element capable of oscillating in-plane; oscillating thephysical element in-plane at a first oscillation frequency, thusinducing a first acoustic field in the fluid sample with a first shearpenetration depth smaller than the size of the analyte in the fluidsample; measuring one or more characteristics of the oscillation of thephysical element at the first oscillation frequency; oscillating thephysical element in-plane at a second oscillation frequencysimultaneously or non-simultaneously with the oscillation at the firstoscillation frequency, thus inducing a second acoustic field in thefluid sample with a second shear penetration depth greater than the sizeof the analyte in the fluid sample; measuring one or morecharacteristics of the oscillation of the physical element at the secondoscillation frequency; determining one or more properties of the fluidsample using one or more of the measured oscillation characteristics,determining the actual concentration of the analyte in the fluid sampleusing one or more of the properties of the fluid sample and optionallyone or more of the measured oscillation characteristics; and calculatingone or more properties of the fluid sample at an arbitrary concentrationof the analyte, wherein the arbitrary concentration of the analyte isdifferent from the actual concentration of the analyte.

In another embodiment, the invention provides a use of a deviceaccording to the invention for the determination of at least one ofviscosity of a fluid sample, viscosity of a bulk phase of a fluidsample, viscosity of a continuous phase of a fluid sample,viscoelasticity of a fluid sample, density of a fluid sample, plasmaviscosity of a blood sample, whole blood viscosity of a blood sample,viscoelasticity of a blood sample, a blood clotting time of a bloodsample, a hematocrit of a blood sample, and a concentration ofanticoagulant in a blood sample.

Additional objects and advantages of the invention will be set forth inpart in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Theobjects and advantages of the invention will be realized and attained bymeans of the elements and combinations particularly pointed out in theappended claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention, as claimed.

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate several embodiments of theinvention and together with the description, serve to explain theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and advantages of this invention may becomeapparent from the following detailed description with reference to theaccompanying drawings in which:

FIG. 1 depicts schematically two embodiments of a substrate layercomprising a suspended element and at least 2 compliant structures,which is suitable for measuring the absolute value of and/or changes inthe viscosity, viscoelasticity and/or density of a fluid sampleindependently and/or before, during and after a reaction. FIG. 1(a)shows an arrangement with a suspended element attached to two compliantstructure undergoing in-plane oscillations. FIG. 1(b) shows anarrangement with a suspended element attached to four compliantstructures undergoing in-plane oscillations.

FIG. 2(a) depicts schematically an embodiment of a physical elementsensing unit. FIG. 2(b) shows an exploded view of a physical elementsensing unit that illustrates the component layers which contributethereto.

FIG. 3(a) shows a schematic view of a test strip for use in determiningthe viscosity, viscoelasticity and/or density of a fluid sample, inparticular a body fluid such as blood. FIG. 3(b) shows an exploded viewof a test strip which illustrates the components therein.

FIG. 4(a) shows a Finite Element Analysis (FEA) simulation of anembodiment (FIG. 2) of the physical element and its in-planeoscillations along the length (x-axis) direction. FIG. 4(b) shows aFinite Element Analysis (FEA) simulation of an embodiment (FIG. 2) ofthe physical element and its in-plane oscillations along the width(y-axis) direction. FIG. 4(c) shows a Finite Element Analysis (FEA)simulation of an embodiment (FIG. 2) of the physical element and itsout-of-plane oscillations (z-axis).

FIG. 5(a) shows a graph detailing the results of a single frequency scanof a physical element undergoing in-plane oscillations with air presentin the chamber, the frequency scan is of the embodiment presented inFIG. 2 between 4100 Hz and 4550 Hz, while FIG. 5(b) shows a graphdetailing the results of a single frequency scan of the same physicalelement undergoing out-of-plane oscillations with air present in thechamber, the frequency scan is between 400 Hz and 800 Hz.

FIG. 6(a) shows a graph detailing the results of a frequency scan ofin-plane oscillations of the physical element immersed in a range ofaqueous (de-ionized water) solutions which contain ethylene glycol indifferent concentrations in order to determine how amplitude andfrequency are affected by the viscosity and density of the liquidsurrounding the oscillating physical element. The percentage valuesindicate the concentration (v/v) of ethylene glycol in deionized water.FIG. 6(b) shows a graph detailing the results of a frequency scan ofout-of-plane oscillations of the physical element immersed in a range ofaqueous (de-ionized water) solutions which contain ethylene glycol indifferent concentrations in order to determine how amplitude andfrequency are affected by the viscosity and density of the liquidsurrounding the oscillating physical element. The percentage valuesindicate the concentration (v/v) of ethylene glycol in deionized water.

FIG. 7(a) shows a graph illustrating the relationship between fluidproperties and response of the physical element undergoing in-planeoscillations i.e. amplitude for ethylene glycol solutions in de-ionizedwater. FIG. 7(b) shows a graph illustrating the relationship betweenfluid properties and response of the physical element undergoingin-plane oscillations i.e. frequency for ethylene glycol solutions inde-ionized water. FIG. 7(c) shows a graph illustrating the relationshipbetween fluid properties and response of the physical element undergoingin-plane oscillations i.e. Q-factor (quality factor) for ethylene glycolsolutions in de-ionized water.

FIG. 8(a) shows a graph illustrating the relationship between fluidproperties and response of the physical element undergoing out-of-planeoscillations i.e. amplitude for ethylene glycol solutions in de-ionizedwater. FIG. 8(b) shows a graph illustrating the relationship betweenfluid properties and response of the physical element undergoingout-of-plane oscillations i.e. frequency for ethylene glycol solutionsin de-ionized water.

FIG. 9(a) shows a schematic of the top of an INReady meter chassis thatis used to interface with a test strip to perform automated measurementof the fluid characteristics of a fluid introduced into the strip'schamber. FIG. 9(b) shows a schematic of the bottom of an INReady meterchassis that is used to interface with a test strip to perform automatedmeasurement of the fluid characteristics of a fluid introduced into thestrip's chamber.

FIG. 10(a) shows the user-interaction work flow of interfacing the stripwith the meter to perform blood based measurements (INR and TEG) viz.strip insertion into meter FIG. 10(b) shows the user-interaction workflow of interfacing the strip with the meter to perform blood basedmeasurements (INR and TEG) viz. meter prompting user to insert blood.FIG. 10(c) shows the user-interaction work flow of interfacing the stripwith the meter to perform blood based measurements (INR and TEG) viz.user collecting blood using a standard lancing device. FIG. 10(d) showsthe user-interaction work flow of interfacing the strip with the meterto perform blood based measurements (INR and TEG) viz. user introducingblood into the chamber through the top opening on the strip.

FIG. 11(a) shows the blood coagulation test INR performed on a sample ofblood with a real-time plot of the instantaneous blood viscositydisplayed on the screen. FIG. 11(b) shows the blood coagulation testsINR and TEG performed on the same sample of blood with a plot of theblood viscoelasticity displayed on the screen.

DETAILED DESCRIPTION OF THE INVENTION Definitions

To facilitate the understanding of this invention, a number of terms aredefined below. Terms not defined herein have meanings as commonlyunderstood by a person of ordinary skill in the areas relevant to thepresent invention. Terms such as “a”, “an” and “the” are not intended torefer to only a singular entity, but include the general class of whicha specific example may be used for illustration. The terminology hereinis used to describe specific embodiments of the invention, but theirusage does not delimit the invention, except as outlined in the claims.

Prothrombin Time (PT) or International Normalized Ratio (INR) test is animportant index for the activity of coagulation factors of the extrinsicpathway—it is the coagulation time when tissue thromboplastin (a tissuefactor) and calcium ion are added into the plasma specimen to inducecoagulation formation. Warfarin and Coumarin are prescribed to slow downthe extrinsic pathway and their effectiveness is measured by the PTtest.

Partial Thromboplastin Time (PTT) test is an indicator of coagulationfactors of the intrinsic pathway, measuring the time whole blood takesto coagulate. PTT is often used as a starting place when investigatingthe cause of a bleeding or thrombotic episode. The PTT test is used todetermine the effectiveness of Heparin therapy prescribed to patientswith perturbations in the intrinsic pathway (typically during invasiveprocedures).

Activated clotting time (ACT) test is used to monitor the effect ofhigh-dose heparin before, during, and shortly after surgeries thatrequire intense anticoagulant administration, such as cardiac bypasssurgery, cardiac angioplasty, and dialysis. It is ordered in situationswhere the partial thromboplastin time (PTT) test is not clinicallyuseful or takes too long.

Thromboelastography (TEG) is a method of testing the efficiency ofcoagulation of blood. It is especially important in surgery,anesthesiology and trauma-related treatment. A small sample of blood(typically 0.36 ml) is placed into a cuvette (cup) which is rotatedgently through 4° 45′ (cycle time 6/min) to imitate sluggish venous flowand activate coagulation. When a sensor shaft is inserted into thesample a clot forms between the cup and the sensor. The speed andstrength of clot formation is measured in various ways and depends onthe activity of the plasmatic coagulation system, platelet function,fibrinolysis and other factors which may be affected by illness,environment and medications.

The quality factor (Q-factor) is a measurement of the “quality” of aresonant oscillating system; it is a measure of the sharpness of theoscillation's resonance or frequency selectivity of a resonant vibratorysystem, measured in a range of frequencies in the vicinity of theresonance oscillation frequency. The Q-factor can be measured bymonitoring the amplitude of oscillation as a function of frequency inthe vicinity of the resonance frequency. The Q-factor can be defined inmultiple ways; a common definition is the ratio of the resonancefrequency to the width of the peak. The width of the resonance peak canbe determined, for example, as the distance between the two frequenciesabove and below the resonance frequency where the amplitude ofoscillation falls to half the magnitude of the amplitude at theresonance frequency, which is generally known as the Full Width Half Max(FWHM).

Shear penetration depth (δ_(s)) is calculated as

δ_(s)=√{square root over (η/pπf)}

where f is the oscillation frequency, η is the viscosity of the fluidsample and p is the density of the fluid sample.

Determination of properties of a fluid, including but not limitedviscosity and density, can be achieved by determining the oscillationcharacteristics of a physical element. The oscillation may correspond toone of the natural or fundamental frequencies of resonance oroscillation of the physical element. The principle of resonance may befurther defined with respect to the function of a tuning fork. When atuning fork is excited by striking it against a surface or an object,its resonating beams or prongs resonate at a certain frequency known asthe fundamental frequency. The fundamental frequency of the prongs isdependent on the physical characteristics of the prongs such as thelength and cross-sectional area of the prong, as well as the materialfrom which the fork is made. More generally, the fundamental frequenciesof resonance or oscillation of any physical element are dependent on thegeometric shape and material properties of the same.

Electromagnetism has been used for inducing and monitoring motion aspart of a variety of applications, for example, in rotors as part ofmotor assemblies. A possible electromagnetic mechanism of actuationinvolves applying an electrical current in the presence of a magneticfield resulting in a motion in the current carrying substrate as aresult of the Lorentz force experienced by the conductor. Lorentz forceF_(L) is defined as the force experienced by a charge q moving with avelocity v in the presence of an electric field E and a magnetic field Bgiven by F_(L)=q[E+(v×B)]. Alternatively, the motion in a moving bodywith a conductive path through it can be detected by electromagneticinduction. Electromagnetic induction is the production of an electriccurrent or voltage across a conductor moving in the presence of amagnetic field. Thus, using the principles of electromagnetism, motioncan be both induced and monitored precisely. Alternatively, actuationmethods such as piezoelectric, capacitive, electromagnetic, and thermalcan be used to induce and monitor motion. Motion can also be monitoredoptically.

In some embodiments of the present invention, a device is provided inwhich the oscillation of a physical element (formed on or part of asubstrate layer), comprising a suspended element suspended by at leasttwo compliant structures attached to the substrate, is configured formonitoring the physical characteristics of a fluid. The physical elementis provided with at least one conductive path running through it, andthe suspended element may have a planar, flat shape. An example of aplanar, flat shape can be a rectangular shape with length and width inthe range of 1 to 10 mm, and thickness less than ⅕^(th) the length orwidth, with the flatness of the element defined by a surface roughnessof less than ⅕^(th) the length or width. The compliant structures mayhave a straight or meandering shape (compare FIGS. 1 and 2). When anactuating signal by way of a current is passed through the physicalelement in the presence of a magnetic field with flux lines intersectingthe physical element, oscillation is induced in the physical element. Ata constant magnetic field, when an electric field via a time-varyingcurrent is applied/injected through the physical element, oscillation isinduced in the physical element. Alternatively, applying a constantelectric field through the physical element in the presence of atime-varying magnetic field can also be used to induce oscillation inthe physical element. Also, the relative direction of the electric andmagnetic fields can target specific oscillations and control theoscillation characteristics (such as amplitude, frequency, etc.) in thephysical element. The oscillation is monitored by measuring thedetection signal i.e. voltage or current induced by electromagneticinduction, in the at least one conductive path through the physicalelement, in a range of frequencies in the vicinity of the oscillationfrequency. In some embodiments of the invention, the actuation anddetection signal are applied and measured across the same or independentconductive paths through the physical element. Alternatively, othermethods including but not limited to optical, piezoelectric, thermal,etc. can be used to monitor the oscillation.

The oscillation induced in the physical element can be at either aresonance or non-resonance frequency of the physical element. In someembodiments of the invention, when the frequency of the time-varyingactuating signal corresponds to one or more of the natural orfundamental frequencies of resonance of the physical element, thecorresponding mode(s) of oscillation is/are induced in the physicalelement. The resonance oscillation characteristics can vary depending onthe physical dimensional structure and material of the physical elementi.e. the suspended element and compliant structures, which can targetspecific frequencies of oscillation.

For example, the suspended element can be flat and rectangular. Giventhe length l and width w of the rectangular element, one can design twospecific frequencies of resonance of the physical element along thelength and width directions, respectively, and the magnitude of theresonance frequencies can be controlled by the corresponding lengths land w. Alternatively, the geometry and structure of the compliantstructures connected to the suspended element can also be configured totailor the resonance oscillation frequencies. In some embodiments of theinvention, the resonance frequencies of oscillation can correspond toin-plane and out-plane modes of oscillation of the physical element. Insome embodiments of the invention, the resonance characteristics of theinduced oscillation in the physical element can be computed bymonitoring the induced detection signal in a range of frequencies in thevicinity of the resonance oscillation frequency. The measureable orquantifiable oscillation characteristics of the physical element includewithout limitation oscillation amplitude, phase, frequency and qualityfactor. In some embodiments of the invention, the actuation signal maycorrespond to a first resonance oscillation that couples to a secondresonance oscillation, and results in both modes of oscillation beinginduced in the physical element. In this case, the detection signal canbe measured in the vicinity of either or both of the induced oscillationfrequencies.

In another embodiment of the invention, the oscillation of the physicalelement can be induced by coupling, interfacing or contacting thesubstrate where the physical element is located with a vibrationinducing actuator which uses one excitation field or a combination ofexcitation fields chosen from (i) piezoelectricity-based mechanical,(ii) capacitive, (iii) electromagnetic, and (iv) thermal excitationfields. In some embodiments of the invention the physical element isprovided with at least one conductive path running through it which maycomprise elements with limited conductivity such as thermal resistors,piezoelectric resistors, etc. For example, a piezoelectric quartzcrystal (PZT) oscillator can be physically affixed to the substrate, andthe PZT oscillator can be driven to induce oscillations in the physicalelement at a particular oscillation frequency. When the PZT oscillatoris driven at a frequency corresponding to one of the natural orfundamental frequencies of resonance of the physical element thecorresponding mode of oscillation is excited. The geometric shape andmaterial properties of the physical element, which may comprise a planarflat element suspended by compliant structures, can be configured forthe natural or fundamental frequency/frequencies of resonance of thephysical element to be a specific value or within a given range offrequencies such as 1 Hz to 1 MHz. The PZT when actuated at these abovementioned frequencies induces resonance oscillations in the physicalelement.

Another embodiment involves applying capacitive fields between thephysical element and one or more isolated, stationary electrode (locatedat a finite distance from the substrate linked to the physical element)to induce oscillations. The capacitive fields can be set up by applyinga time-varying voltage signal between the conductive path runningthrough the physical element and the stationary electrodes. Resonanceoscillations in the physical element can be induced by applying atime-varying voltage at the natural or fundamental frequencies of thephysical element.

In yet another embodiment, thermal resistors are provided as part of theconductive path running through the physical element. Oscillations inthe physical element corresponding to its natural or fundamentalfrequencies of resonance can be induced by heating the resistors bypassing current through the conductive path running through the physicalelement. By applying a time-varying current signal, steady-state ortransient oscillations can be induced in the physical element.

In another embodiment of the invention, the oscillation induced in thephysical element is detected by one detection field or a combination ofdetection fields chosen from (i) piezoelectricity-based electrical, (ii)capacitive, (iii) electromagnetic, (iv) thermal and (v) opticaldetection fields arising due to the oscillation. For example, when apiezoelectric quartz crystal (PZT) oscillator affixed to the substrateis used to induce oscillations in the physical element, the oscillationcharacteristics can be monitored by measuring the PZT's electrical inputcharacteristics in a frequency range in the vicinity of the oscillationfrequency excited in the physical element.

Alternatively, one or more piezoelectric resistors can be provided aspart of the conductive path running through the physical element, whichexhibit a change in resistance due to the oscillation of the physicalelement. The oscillation can be monitored by incorporating thepiezoelectric resistors as part of a Wheatstone bridge circuit andmeasuring the bridge voltage in a frequency range in the vicinity of theoscillation frequency excited in the physical element.

In yet another alternative, one or more thermal resistors are providedas part of the conductive path running through the physical element thatcan measure the change temperature due to the oscillation of thephysical element. The thermal resistors can be made of pyroelectricmaterials which have the ability to induce a voltage with a change intemperature. The oscillations in the physical element can be monitoredby measuring the change in voltage across the resistors in a frequencyrange in the vicinity of the oscillation frequency excited in thephysical element.

In yet another alternative, an optical sensor module is used to directan optical signal onto the physical element and monitor the reflectedoptical signal using a photodetector. The oscillations in the physicalelement can be monitored by measuring the photodetector output signal inthe vicinity of the oscillation frequency excited in the physicalelement. Alternatively, a photodetector module can be incorporated onthe physical element as part of the conductive path running through it.When an optical signal is directed onto the photodetector, theoscillation in the physical element can be monitored by measuring thechange in the photodetector output in a frequency range in the vicinityof the oscillation frequency excited in the physical element.

When a fluid sample is present in the chamber with the physical element,the effect(s) (e.g., damping) on the oscillations in the physicalelement can be used to determine one or more physical characteristics ofthe fluid such as viscosity and density. In some embodiments of theinvention, the oscillation induced in the physical element can be at anon-resonance frequency. The measureable or quantifiable oscillationcharacteristics of the physical element include without limitationoscillation amplitude, phase, frequency and quality factor. In allresonating devices, the quality factor is affected by the surroundings;the quality factor of a resonant system changes according to theviscosity, viscoelasticity and density of the media in which itoscillates. The amplitude of the oscillating element is proportional tothe fluid viscosity; in a low viscosity fluid, the element willoscillate with much higher amplitude over a narrow frequency range nearthe natural or fundamental frequency, compared to when in a highviscosity fluid. Introduction of a fluid sample in the vicinity of thephysical element causes damping in its oscillation characteristics, andchanges in amplitude, frequency and/or quality factor are indicative ofthe viscosity, viscoelasticity and density of the fluid. In someembodiments of the invention, the conductive path through the physicalelement comprises one or more heating elements, including but notlimited to for example, one or more resistive track heaters, to controlthe temperature of the fluid medium in the chamber, and/or one or moresensing elements, to monitor the temperature of the fluid medium in thechamber.

In some embodiments of the invention, when the physical element issurrounded by a biological fluid which can undergo a reaction leading tocoagulation, the resonating element is further dampened by theincreasing viscosity of the fluid sample as it coagulates. This dampingeffect can be measured periodically (i.e., at two or more time points)to determine the coagulation of the body fluid as a function of time. Insome embodiments of the invention, the biological fluid comprises bloodor plasma. In some embodiments, the coagulation is initiated by physicalcontact with negatively charged substrates or by the addition of bloodcoagulation-inducing compounds, for example, thromboplastin, and thetime to formation of the blood clot can be accurately determined as partof blood tests such as Prothrombin Time (PT), Partial ThromboplastinTime (PTT), Activating Coagulation Time (ACT), etc.

In another embodiment of the invention, one or more physical elementsare present in a chamber, defining an internal volume which is suitablefor receiving and retaining a fluid sample, and the one or moresuspended elements are configured to oscillate upon application of anactuating signal.

In some embodiments of the invention, the internal volume of the chamberis configured to receive and hold the fluid sample in place before fluidproperty measurement is performed. The chamber is formed by a pluralityof layers such that there exists at least one layer above (uppersubstrate) and one layer below (lower substrate) the chamber, such thatthe substrate layer comprising the physical element is in between thelayers. The substrate layer may generally be parallel to the layersabove and below the chamber, except to the extent of out-of-planeoscillations of the physical element of the substrate layer during whichthe physical element (including the suspended element and/or compliantstructures) is deformed from a parallel configuration.

As discussed earlier, the fluid characteristics can be determined fromoscillation characteristics of the physical element. Alternatively, theentire structure composed of the physical element and chamber formed bythe upper and lower substrates, can be oscillated at a correspondingresonance or non-resonance frequency to determine the fluidcharacteristics such as the fluid density. The additional mass of thefluid once introduced in the chamber dampens the oscillation of theentire structure and subsequently shows reduction in measureableoscillation characteristics such as oscillation amplitude, frequency andQ-factor.

In-Plane Vibration

One method of measuring viscosity of a fluid involves trapping the fluidbetween a fixed and moveable parallel plates or planar structures, andmonitoring the drag experienced by the moveable planar structure when itis moved in its own plane at a constant velocity relative to the fixedplanar structure. The fluid experiences a true shear stress resulting ina shear strain on the fluid, and the fluid viscosity is computed asdetermined by the ratio of the stress applied to the strain experiencedby the fluid.

Miniaturized microacoustic sensors like quartz thickness shear moderesonators (TSM) and surface acoustic wave (SAW) devices have beensuccessfully used as alternatives to traditional viscometers, but thesedevices measure viscosity at relatively high frequencies and smallvibration amplitudes. Since the penetration depth (δ_(s)=√{square rootover (η/9πf)}) of the shear waves excited by these sensors are small(due to high frequencies), only a thin film of liquid close to thedevice is probed. In addition due to the small penetration depth thesesensors are unable to detect the presence and effect of particles(size>δ_(s)) in complex or non-Newtonian fluids, and can only measurethe viscosity of the continuous phase of the fluid. Finally, the smallervibration amplitude in these sensors results in lower measurementsensitivity.

In devices and methods according to the present invention, the physicalelement can be configured so that the suspended element has at least onenatural or fundamental frequency of vibration corresponding to anin-plane oscillation. When a fluid sample is introduced and confined inthe chamber containing the physical element, the oscillation induced inthe physical element applies a true shear stress to the fluid trappedbetween the physical element and the upper & lower layers. By measuringvibration characteristics of the physical element, which can be furthertranslated into the shear rate and shear stress experienced by thefluid, the fluid viscosity can be determined. In some embodiments of theinvention, the physical element's in-plane oscillation can be tailoredto be sensitive to the fluid density and hence, the fluid density can bedetermined from the damping of oscillation characteristics. This deviceand methodology offer high-accuracy measurement of the absolute andinstantaneous value of the fluid viscosity in a small fluid sample.

In one embodiment of the invention, based on the geometric design,structure and material properties of the physical element theoscillation frequency can be relatively low, such as in the range of afew Kilo-Hertz or less (e.g., less than or equal to 5, 4, 3, 2, or 1kHz), resulting in a relatively large shear penetration depth into thefluid under concern. Also, higher oscillation amplitudes can be achievedresulting in higher sensitivity to fluid viscosity. In anotherembodiment of the invention, the physical element can have at least twoin-plane oscillation modes, one with a low frequency (see above) and theother with high frequency (e.g., 10 KHz or more), thus having twodistinct oscillation modes with large and small shear penetration depthsrespectively. In a fluid comprising discrete components/additives,including non-Newtonian fluids, the oscillation corresponding to a shearpenetration depth smaller than the size of the discretecomponents/additives can be used to determine the fluid viscositycorresponding to the continuous phase, and shear penetration depthlarger than the size of the discrete components/additives can be used todetermine the bulk viscosity of the fluid. In some embodiments of theinvention, the size of the discrete components/additives can be a numberin the range of 0.5 to 500 μm. “Size” may refer to the hydrodynamicdiameter or the largest physical dimension measured along standardCartesian coordinates. These two in-plane oscillation modes can beinduced in the physical element simultaneously or in sequence, thusenabling the measurement of the viscosity of the continuous and bulkphases of complex or non-Newtonian fluids. In some embodiments of theinvention, the amplitude of vibration induced in the physical elementcan be controlled by increasing the amplitude of actuation subsequentlycontrolling the shear rate ({dot over (γ)}) applied to the fluid. Insome embodiments of the invention, where electromagnetic actuation isemployed the amplitude of vibration can be changed by changing themagnitude of current through the conductive path and/or the magneticfield applied. Thus fluid viscosity at varying shear rates can bedetermined for complex or non-Newtonian fluids.

In some embodiments, the device can be configured so that the physicalelement oscillation induces a first acoustic field in the fluid samplewith a first shear penetration depth smaller than a threshold value,wherein the threshold value ranges from 0.5 microns to 500 microns, andoscillation at the second oscillation frequency induces a secondacoustic field in the fluid sample with a second shear penetration depthgreater than the threshold value. In some embodiments, the first andsecond shear penetration depths differ by at least a minimum amount,which may be a value greater than or equal to 0.5, 1, 2, 3, 4, 5, or 10microns, or a value ranging from 0.5 to 1, 1 to 2, 2 to 3, 3 to 4, 4 to5, or 5 to 10 microns.

In some embodiments of the invention, when a biological fluid such asblood is introduced in the chamber, the two in-plane oscillation modescan have penetration depths greater or smaller than the average size ofthe red blood cells which form the discrete component in the sample. Insome embodiments of the invention, the two in-plane oscillation modescan have penetration depths greater or smaller than 5 μm, whichcorresponds to a lower limit of the size of red blood cells. In someembodiments of the invention, the two in-plane oscillation modes canhave penetration depths greater or smaller than 10 μm, which correspondsto an upper limit of the size of red blood cells. As discussed above,the two in-plane oscillation modes can be used to measure the viscosityof the plasma (continuous phase) and whole blood (bulk phase) of theblood sample simultaneously or in sequence. In some embodiments of theinvention, when a body fluid such as blood is introduced in the chamber,the two in-plane oscillation modes can have penetration depths greateror smaller than the average size of platelets which form the discretecomponent in the sample. In some embodiments of the invention, the twoin-plane oscillation modes can have penetration depths greater orsmaller than 2 μm, which corresponds to a lower limit of the size ofplatelets. In some embodiments of the invention, the two in-planeoscillation modes can have penetration depths greater or smaller than0.5 μm, which corresponds to a size of some macromolecules ormacromolecular assemblies, where the size is defined by the hydrodynamicdiameter of the molecule.

The chamber of devices according to the invention defines an internalvolume which is suitable for receiving and retaining a fluid sample, andalso accommodates at least one physical element in a manner which allowsfor the motion or oscillation of the suspended element and attachedcompliant structures. The motion or oscillation can occur in anunimpeded manner, i.e., occupying any of the range of space traversedduring the oscillation does not result in collision or contact of thephysical element with other solid material. To be clear, “unimpeded”does not mean “without any resistance at all”; fluid, when present,provides a degree of resistance to or damping of to oscillation, and thecompliant structures may provide a restoring force when the suspendedelement is displaced from resting position, and the presence ofresistance from fluid, restoring force from the compliant structures,and the like are entirely consistent with “unimpeded” motion oroscillation as used herein. The chamber is defined by means of upper andlower layers positioned above and below the substrate layer, whichcomprises the physical element enclosed inside the chamber; thesubstrate layer may be formed, patterned, or otherwise assembled orconstructed to comprise the physical element. In some embodiments of theinvention, the substrate is affixed to the upper and lower substrates bymeans of intermediary layers in all areas except for the physicalelement enclosed inside the chamber, thus effectively restricting motionof the substrate to the physical element alone. In some embodiments ofthe invention, the chamber can include multiple physical elements in thesame substrate or in multiple substrates as part of the plurality oflayers in the device.

In another embodiment of the invention, when oscillation is induced inthe physical element a shear-wave field is induced in the fluid retainedin the chamber. The device can be configured such that the distancebetween at least one of the upper and lower substrate layers and thephysical element (D) has a standing shear-wave field induced in thefluid medium between the upper and/or lower substrates and the suspendedelement during oscillation. In order to have a consistent and reliablestanding shear-wave field induced, the distance D can be smaller than orequal to the shear penetration depth (δ_(s)=√{square root over(η/9πf)}). For example, if the fluid medium is water with density of 1gm/cc and viscosity of 1 cP and a oscillation frequency of 1 KHz, thedistance D should be smaller than or equal to δ_(s)=17.84 μm. the lowerthe ration of the distance D to the shear wavelength (λ_(s)) of thefield induced in the medium surrounding the physical element, the higheris the consistency and uniformity of the acoustic field set up in thefluid medium, where λ_(s)=2πδ_(s)/√{square root over (2 )}cos(δ_(l)/2)where δ_(s) is the shear penetration depth (δ_(s)=√{square root over(η/pπf)}) and δ_(l) is the loss-tangent angle of the fluid medium.

The distance D is adjustable or permanently fixed depending on theproperties of the surrounding medium. In some embodiments of theinvention, the distance D can be adjusted by means of intermediatelayers between the substrate comprising the physical element and theupper and/or lower substrates. The intermediate layers can be composedof flexible materials such as foam, polymeric substrates, etc., suchthat the intermediate layer thickness can be varied by applyingcompression to the device in the thickness direction. The compressionpressure can be performed offline before measurement depending on thefluid sample, or in real-time with the fluid under concern introducedinto the device and monitoring the standing shear-wave field induced inthe fluid. In some embodiments of the invention, the distance D can beadjusted by physically moving the upper & lower substrates closer to orfarther away from the physical element by an automated assembly,followed by filling of the region around the physical element betweenthe substrate containing the physical element and the upper & lowersubstrates in order to form the chamber. The filling material can be onethat can flow and change state from a fluid to solid including but notlimited to epoxy, etc. In some embodiments of the invention, theacoustic field setup in the fluid trapped between the physical elementand the chamber walls can be used to not only determine the viscosity ofthe fluid but also its viscoelastic properties. Also, the presence ofthe fixed chamber walls close to the oscillating physical element offersadditional benefits for high accuracy monitoring of the change inphysical properties of the fluid as a function of time during gelformation.

In some embodiments of the invention, when a biological fluid such asblood is introduced in the chamber and undergoes a coagulation reaction,the blood clot formed between the physical element and the chamber wallscan be used to compute the viscoelastic properties of the blood clot. Insome embodiments of the invention, the viscoelastic properties of bloodundergoing coagulation can be monitored as a function of time and bloodtests, e.g., a thromboelastogram (TEG), can be performed.

Out-Plane Vibration

In another embodiment of the invention, the suspended element can haveat least one natural or fundamental frequency of vibration correspondingto an out-of-plane oscillation. When a fluid sample is introduced andconfined in a chamber containing the physical element, the oscillationcharacteristics are damped. The density of the fluid can be determinedby monitoring the oscillation characteristics such as oscillationamplitude, phase, frequency and quality factor. Frequency and othercharacteristics may be measured as a change in oscillation frequencyupon addition of the fluid sample to the chamber. In addition, thephysical element's out-of-plane oscillation can be tailored to besensitive to the fluid density and hence, the fluid density can bedetermined from the damping of oscillation characteristics. In someembodiments of the invention, the fluid density measured can be used toidentify the concentration of at least one discrete component/additivein a fluid. The discrete components/additives can be, for example,macromolecules, macromolecular complexes (e.g., cytoskeletal filaments),red blood cells, platelets, particulates or solid-phase objects. In someembodiments of the invention, the physical element oscillation can beconfigured for measurement of the density of the continuous phase andbulk phase of the fluid independently using the same or differentresonance oscillation mode of the physical element.

In another embodiment of the invention, the physical element can enablethe measurement of the fluid's continuous phase viscosity, bulkviscosity and density. In some embodiments of the invention, astandardized measure of bulk viscosity of a fluid can be determined as afunction of one or more of viscosity of continuous phase, bulk phase,fluid density and concentration of discrete component/additive (if any).Further, the static or dynamic viscoelastic properties of a fluid as afunction of time can be determined from the measured (orstandardized-measures) viscosities of the fluid at different appliedshear rates using various theoretical or empirical models. For example,from the bulk viscosity measured at varying shear rates can be used withCasson's model given by, η=(√{square root over (τ_(y))}+√{square rootover (k{dot over (γ)})})/{dot over (γ)} where τ_(y) is the yield stressof the fluid, {dot over (γ)} is the shear rate applied to fluid and k isa constant, to determine a value for τ_(y) and k by statistical methodssuch as regression analysis.

In another embodiment of the invention, where the fluid under concern isblood introduced into the chamber, the physical element can be used tomeasure the plasma viscosity (η_(plasma), continuous phase), whole bloodviscosity (η_(WBV), bulk phase) and blood density when exposed to ablood sample. The blood density measured can be used to identify theconcentration of red blood cells or hematocrit (Hct) in the sample.Since whole blood viscosity is highly dependent on the plasma viscosityand hematocrit, in order to identify the normalcy or abnormality ofblood viscosity of different individuals the blood viscosity needs to bestandardized or corrected to a fixed hematocrit (0.45 is generallyused). The formula for the standardized or corrected whole bloodviscosity at a fixed hematocrit of 0.45 is given by—

$\left( \frac{\eta_{{WBV} - 0.45}}{\eta_{plasma}} \right) = \left( \frac{\eta_{{WBV} - {Hct}}}{\eta_{plasma}} \right)^{0.45/{Hct}}$

where η_(WBV-0.45) is the standardized or corrected whole bloodviscosity at a hematocrit of 0.45, η_(WBV-Hct) is the whole bloodviscosity at hematocrit Hct, and η_(plasma) is the plasma viscosity.

In another embodiment of the invention, the chamber along with thesubstrate comprising the physical element can be incorporated in adisposable test strip. The chamber is so assembled to have the one ormore physical elements in the substrate layer suspended inside thechamber, while another part of the substrate layer is affixed to upperand lower substrates above and below the chamber, as part of a pluralityof layers stacked to form the test strip. Further, the chamber can becomposed of a plurality of layers patterned/formed in order to have itswalls positioned closely together to form a capillary. The materialschosen to create the surfaces of the chamber can be selected to providea low surface tension and/or contact angle (e.g., less than or equal to45 degrees) which allows the chamber to fill by a capillary action.These materials are selected as they enhance liquid filling withoutinterfering with the reaction. Examples of such materials will be wellknown to the person skilled in the art. In some embodiments of theinvention, the upper and lower substrate layers of the chamber cancomprise a plurality of components, including but not limited toelectrically conductive paths to perform electrochemical analysis and/orto detect the presence of an analyte in the fluid and/or the fluiditself in the chamber. In some embodiments of the invention, theelectrically conductive paths can be used to perform electrochemicaldetection of sugar levels in the blood sample introduced into thechamber [13]. In some embodiments of the invention, the upper and lowersubstrate layers can further comprise electrically conductive pathswhich contain one or more heating elements, such as resistive trackheaters, and/or one or more temperature sensors, to control and monitorthe temperature of said chamber, respectively.

In some embodiments, a fluid sample may be introduced into the chamberwherein the fluid sample begins undergoing a chemical reaction soonafter its addition. For example, the chamber may contain an agent thatreacts with the sample once it is present, or an agent can be added tothe sample once it is present, or one or more of the surfaces of thechamber may promote or catalyze a reaction in the fluid sample. When afluid is introduced and confined to the chamber housed inside the teststrip, the oscillation characteristics (amplitude, phase, frequency,Q-factor, etc.) of the physical element will generally stabilizemomentarily, before further changes take place due to the chemicalreaction, allowing for rapid determination of physical characteristicsof the fluid. The fast response time of the sensor can allow for theaccurate identification of the time at which the fluid sample wasintroduced to the chamber.

The substrate layer comprising the physical element can be made of anysuitable inert material and may be selected from amongst others:polymers such as polyester (PET), plastics, etc. The substrate layer canbe fabricated using mass manufacturing methods including but not limitedto roll-to-roll continuous flow manufacturing. The physical elements canbe formed or patterned by etching, laser treatment or by mechanicalpunching of the substrate layer. The electrically conductive pathsthrough the physical elements can be made by means of patternedconductive paths on the substrate layer that form circuits such as inthe case of printed circuit boards. The conductive circuits can be ofany suitable conductive material and may be selected from, but notlimited to conductive polymers, gold, platinum, copper or silver. Theconductive paths can be patterned by several methods such as laserablation, or by screen printing. Further, the conductive paths can beinsulated from the fluid by deposition of insulating layers on theconductive paths or, have the conductive layer embedded within thesubstrate with the physical element.

In some embodiments of the invention, the conductive paths can beexposed to the fluid allowing for electrochemical analysis and/ordetection of the presence of an analyte in the fluid and/or the fluiditself in the chamber. In some embodiments of the invention, theconductive paths can be used to perform electrochemical detection ofsugar levels in a blood sample introduced into the chamber. Theconductive paths would serve to form a closed electrical path throughthe physical element. In some embodiments of the invention, thesubstrate comprising the physical element can be made of a substantiallymetallic material also serving the additional functional purpose of anelectrically conductive path through the physical element.

In other embodiments, the suspended element is not substantiallymetallic. For example, the metal content of the suspended element may beless than 50%, 40%, 30%, 20%, 10%, 5%, or 1% by weight. Configurationsof the device in which the suspended element is not substantiallymetallic can provide beneficial properties. For example, the substratecan be made of polyester and the conductive paths can be formed byprinting conductive ink onto the polyester substrate. Use of a suspendedelement which is not substantially metallic makes it possible to controlthe geometry of the polyester substrate and the conductive pathsindependently, consequently enabling greater control over theoscillation characteristics of the suspended element than if the elementwere substantially metallic. Additionally, polyester, being flexible, iscompatible with high-volume roll-to-roll continuous flow manufacturingprocesses, which can be beneficial to the cost-effective manufacturingof the substrate, e.g., as part of a disposable test strip.

In some embodiments of the invention, the substrate layer on which thephysical element is disposed can be patterned by laser cutting a sheetof polyester, onto which the conductive path is printed in a specificpattern to provide conductivity through the physical element. Conductiveinks such as silver-ink, Palladium-ink, etc. can be used for printingthe conductive path on the substrate layer.

In certain embodiments, a series of edge connectors on the disposablestrip could be provided to allow direct contact or connection between atest meter and the physical elements. An additional purpose of theconductive circuit would be to activate the device in readiness toreceive a fluid sample, by means of bridging contacts provided by theedge connectors. Alternatively, the physical elements could be excitedand/or monitored by non-contact means such as acoustic wave amplitudereflection, light beams or radio frequency. The separate layers of thetest strip could be aligned such that no further trimming or adjustmentto their size and/or outer peripheral surface would be necessary.However, a plurality of devices could be produced and trimmed to thedesired size and shape of the disposable test strip.

In another embodiment of the invention, the fluid under concern is abiological fluid, in particular blood. The chamber can be provided witha reagent comprising at least one blood clotting agent in an amountsuitable to induce coagulation of a blood sample in the chamber. In someembodiments of the invention, the reagent is present in dry form in thechamber. The reagent can be added to the chamber before or aftercompletion of assembly of the strip. Further, the reagent can beprovided on the physical element of the substrate layer and housedinside the chamber. In some embodiments of the invention, the reagent isadded to the chamber prior to or after the introduction of blood. Insome embodiments of the invention, the reagent is comprised of one or acombination of anticoagulants (such as Heparin, Warfarin, etc.),viscosity-changing molecules (such as Dextran) and Coagulation factormolecules that can induce coagulation. Generally, Coagulation factormolecules include naturally occurring or synthesized compounds thateither promote or inhibit blood coagulation including but not limited toFactor I, II, III, IV, V, VI, VII, VIII, IX, X, XI, XII, XIII, vonWillebrand factor, prekallikrein, high-molecular-weight kininogen,fibronectin, antithrombin III, heparin cofactor II, protein C, proteinS, protein Z, protein Z-related protease inhibitor, plasminogen, alpha2-antiplasmin, tissue plasminogen activator (tPA), urokinase,plasminogen activator inhibitor-1 (PAII), plasminogen activatorinhibitor-2 (PAI2) and cancer procoagulant. Generally,“viscosity-changing molecules” include compounds that alter theviscosity of blood by at least 0.001 cP upon introduction into blood ofthe amount actually added to the blood or present in the chamber. Inother embodiments, the above mentioned reagents can be present in thefluid as it is introduced into the chamber and need not necessarily bepresent in the device as it stands. For example, a reagent could bepresent in a blood sample as a result of having been administered to theindividual who supplied the blood. In another embodiment, the devicecomprises multiple chambers in which the reagent is provided,accommodating at least one substrate with one or more physical elementsin each chamber. Further, the same blood sample can be directed andsplit into multiple microfluidic paths leading to the different chambersin the device. Thus, blood coagulation can be induced and monitored atdiscrete regions of the device in the same blood sample.

In some embodiments of the invention, when a biological fluid such asblood is introduced in the chamber, two in-plane oscillation modes canhave penetration depths greater or smaller than the average size of redblood cells which form a discrete component in the sample. In someembodiments of the invention, the two in-plane oscillation modes canhave penetration depths greater or smaller than 5 μm, which correspondsto an approximate lower limit of the size of red blood cells. Asdiscussed above, the two in-plane oscillation modes can be used tomeasure the viscosity of the plasma (continuous phase) and whole blood(bulk phase) of the blood sample simultaneously or in sequence. In someembodiments of the invention, when a biological fluid such as blood isintroduced in the chamber, the two in-plane oscillation modes can havepenetration depths greater or smaller than the average size of plateletswhich form a discrete component in the sample. In some embodiments ofthe invention, the two in-plane oscillation modes can have penetrationdepths greater or smaller than 2 μm, which corresponds to a lower limitof the size of platelets. In some embodiments of the invention, the twoin-plane oscillation modes can have penetration depths greater orsmaller than 0.5 μm, which corresponds to the approximate size of somemacromolecules and/or macromolecular complexes. As discussed earlier,the two penetration depths may differ by at least a minimum amount or byan amount in a given range.

In another embodiment of the invention, where the fluid under concern isblood introduced into the chamber, the physical element is configured tomeasure the plasma viscosity (η_(plasma), continuous phase), whole bloodviscosity (η_(WBV), bulk phase) and blood density when exposed to ablood sample. The blood density measured can be used to identify theconcentration of red blood cells or hematocrit (Hct) in the sample.Since whole blood viscosity is highly dependent on the plasma viscosityand hematocrit, in order to identify the normalcy and abnormality ofblood viscosity of different individuals the blood viscosity needs to bestandardized or corrected to a fixed hematocrit (0.45 is generallyused).

In some embodiments of the invention, the biological fluid comprises ofblood or plasma and coagulation can be initiated by physical contact tonegatively charged substrates or the addition of bloodcoagulation-inducing compounds including but not limited tothromboplastin. Thus, a blood coagulation-inducing compound such asthromboplastin may be present in a device according to the invention,including before addition of blood or plasma, and used in methodsaccording to the invention. Alternatively, the bloodcoagulation-inducing compound such as thromboplastin may be added toblood or plasma present in the chamber. The plasma, whole bloodviscosity and/or density of the sample can be monitored before, duringand/or after the coagulation reaction. Further, the time to formation ofa blood clot can be determined as part of blood tests including but notlimited to Prothrombin Time (PT), Partial Thromboplastin Time (PTT),Activating Coagulation Time (ACT), etc. In some embodiments of theinvention, when a biological fluid such as blood is introduced in thechamber and undergoes a coagulation reaction, the blood clot formedbetween the physical element and the chamber walls can be used tomeasure the viscoelastic properties of the blood clot. In someembodiments of the invention, the viscoelastic properties of bloodundergoing coagulation can be monitored as a function of time and bloodtests such as a thromboelastogram (TEG) can be performed. In someembodiments of the invention, the hematocrit computed in the bloodsample by way of the measured blood density can be used to calibrate theabove mentioned blood coagulation tests (PT, PTT, ACT, TEG, etc.)performed.

Monitoring or reading of a device according to the invention in order toprovide an automated means for determining the viscosity,viscoelasticity and/or density of a fluid sample can be provided by theuse of a machine, such as a metering device, which can interact with thesensor device of the invention in a manner which allows for the meter todetermine the results of the sample testing. In some embodiments of theinvention, the metering device comprises one or more of the following:processor, bus, input interface such as keypad or data port, inputinterface such as a resistive or capacitive touch-screen display, outputinterface such as display screen, output interface such as a data port,wireless connectivity for input and/or output interface, power supplysuch as battery or power cord or power receptacle, strip connectorinterface for providing conductivity, etc. In some embodiments of theinvention, where the sensor device is connected to, or engaged with ameter, this provides an automated means for determining the physicalcharacteristics of a fluid including but not limited to viscosity,viscoelasticity and/or density. For example, where the meter isconnected to the sensor device, the meter could bereleasably/temporarily engaged with the test strip and would have theability to output the test results, typically by means of a visualdisplay or readout. In addition, where the meter processes the datareceived from the sensor device, the meter may process this informationand apply correction factors which would take into account any batch tobatch variability associated with the disposable test strip manufacture.

In some embodiments of the invention, the meter may include electroniccomponents as part of a processor unit which is configured to induce anddetect the oscillation of the physical element. When the meter isconnected to the sensor device, electrical conductivity is establishedbetween the processor unit and the conductive paths through the one ormore physical elements in the sensor device. In some embodiments of theinvention, oscillation at a particular frequency is induced in thephysical element by the processor unit applying a time-varying actuationsignal such as a voltage/current corresponding to the oscillationfrequency through one or more conductive paths in the physical element.Similarly, a time-varying detection signal, such as a voltage/current,is measured by the processor unit through one or more conductive pathsin the physical element in the vicinity of the oscillation frequency. Insome embodiments of the invention, when the oscillation corresponds to anatural or fundamental resonance frequency of the physical element, theresonance characteristics are determined by actuating and detecting theoscillation in the physical element in a range of frequencies in thevicinity of the resonance frequency, for example, within a factor of1.5, 2, 3, 4 or 5 of the resonance frequency. The resonancecharacteristics measured can include but are not limited to resonanceamplitude, resonance frequency, Q-factor, etc. In some embodiments ofthe invention, where the oscillation in the physical element is inducedand/or detected using electromagnetism, the actuating signal provided bythe processor unit corresponds to a current injected/applied in therange of 100 nA to 10 A, for example, 100 μA to 1 A, through theconductive paths in the physical element in the presence of a magneticfield in the range of 0.001 T to 10 T, for example, 0.01 T to 2 T. Insome embodiments, the detection signal measured by the processor unitcorresponds to a voltage in the range of 0.01 μV to 10 V, for example, 1μV to 1 V, in the presence of a magnetic field in the range of 0.001 to10 T or 0.01 T to 2 T. In some embodiments, the amplitude of oscillationinduced in the physical element is in the range of 1 nanometer to 100microns, for example, 10 nanometers to 10 microns. The meter is providedwith one or more enclosures to accommodate one or more permanent orvariable magnets (such as an electromagnet) in the vicinity of aconnector that provides conductivity to the one or more physicalelements in the sensor device. In some embodiments of the invention, themeter is provided with top and bottom halves forming part of aclam-shell based assembly, that allows for the touchscreen display forthe input and output interface, connector to the sensor device and themagnet to be enclosed in the top half, and the processor unit, battery,data port and power cord receptacle in the bottom half. The top andbottom halves can comprise one or more alignment fixtures that allow forprecise assembly and securing or fastening of the two halves using meanssuch as snap-fit assembly, screw-based compression assembly, etc.

In some embodiments of the invention, the meter may include a facilityto sample environmental conditions such as temperature and apply acorrection factor to the measurement response. Additionally the metercan have a memory facility that would allow previous readings to bestored and recalled, for example to provide a comparison of measurementsacross two or more dates or times. This feature may be of particularutility to an individual who undergoes regular testing as part of themonitoring of anti-coagulant levels such as Warfarin, Heparin, etc. inthe blood. In some embodiments of the invention, in order to calibratethe machine or the individual sensor device, the meter may perform aninitial self-test on the disposable strip prior to blood introduction.

FIGS. 1(a) and 1(b) show schematics of two embodiments of substratelayers of the sensor devices of the invention which contain the physicalelement comprising the suspended element and compliant structures, theoscillation of which is used to determine the viscosity, viscoelasticityand/or density of a fluid, typically a liquid.

According to the first embodiment, as shown in FIG. 1 (a), a substratelayer comprises a “physical element” (e.g., as a result of having beenmachined to form the physical element), which comprises a suspendedelement 101 and compliant structures 102, the compliant structures beingattached to the suspended element at one end and the main body of thesubstrate layer 104 at the other. The main body of the substrate layer104 is maintained to be stationary, indicated by the “X” mark across thestructure, such that the physical element is configured to performunimpeded motion or oscillations upon actuation. Also, the main body ofthe substrate layer 104 can be relatively larger than the suspendedelement 101. An electrically conductor 103 is formed and patterned onthe substrate layer such that there is a conductive path through thephysical element. A magnetic field 106 is applied in a directionperpendicular to the plane of the substrate layer. A time-varyingcurrent applied through the conductor 103 in the presence of a constantmagnetic field 106 causes the physical element to oscillate in-plane;oscillation may be at the fundamental frequency or at a harmonicfrequency of the physical element. Alternatively, a magnetic field 106applied in the same plane as that of the physical element causes thephysical element to oscillate out-of-plane; again, oscillation may be atits fundamental frequency, or at a harmonic frequency. The in-planeoscillations induced are indicated by the dotted line 105. Theoscillation of an electrical conductor 103 in the presence of themagnetic field 106 electromagnetically induces a “detection voltage”,which can be used to ascertain the characteristics of physicaloscillatory movement in the structure. The shape and geometry of thesuspended element 101 and compliant structures 102, and the exactlocation of the compliant structure relative to the suspended elementand the stationary substrate layer 104 may be selected to obtain theoptimum sensitivity for the measurement of fluid properties, ascertainedby methods such as finite element analysis, empirical analysis,theoretical analysis, trial and error, etc. In addition, the geometrycan be consistent with a relatively low or high oscillation harmonicfrequency, resulting in a relatively large or small shear penetrationdepths (δ_(s)=√{square root over (η/pπf)}) into the fluid under concernrespectively. Also, the amplitude of oscillation induced in the physicalelement can be controlled by the current applied through the conductor103 subsequently controlling the shear rate ({dot over (γ)}) applied tothe fluid.

In the embodiment of the substrate layer shown in FIG. 1(b), analternative arrangement for the physical element is provided. Thephysical element is comprised of the suspended element 107 and twocompliant structures 108 and 109 on each side of the symmetry line ofthe structure, the compliant structures being attached to the suspendedelement at one end and the main body of the substrate layer 115 at theother. The main body of the substrate layer 115 is maintained to bestationary, indicated by the “X” mark across the structure, such thatthe physical element is allowed to perform unimpeded motion oroscillations. Also, the main body of the substrate layer 115 can berelatively larger than the suspended element 107. Two electricalconductors 110 and 111 are formed and patterned on the substrate layersuch that there are two independent and isolated conductive pathsthrough the physical element. A magnetic field 114 is applied in adirection perpendicular to the plane of the substrate layer. Atime-varying current applied through one or both conductors 110 and 111in the presence of a constant magnetic field 114 cause the physicalelement to oscillate in-plane; oscillation may be at the fundamentalfrequency or at a harmonic frequency of the physical element.Alternatively, a magnetic field 114 applied in the same plane as that ofthe physical element causes the physical element to oscillateout-of-plane; oscillation may be at the fundamental frequency or at aharmonic frequency of the physical element. The in-plane oscillationsinduced are indicated by the dotted line 113. The oscillation of theelectrical conductors 110 and 111 in the presence of the magnetic field114 electromagnetically induces a “detection voltage”, which can be usedto ascertain the characteristics of physical oscillatory movement in thestructure. The time-varying current and the detection voltage can beapplied through either one of the electrical conductors 110 and 111 thusisolating the actuation and detection signals reducing crosstalk orinterference. The shape and geometry of the suspended element 107 andthe number of compliant structures 108 and 109, and the exact locationof the compliant structures relative to the suspended element and thestationary substrate layer 115 may be selected to obtain the optimumsensitivity for the measurement of fluid properties, ascertained bymethods such as finite element analysis, empirical analysis, theoreticalanalysis, trial and error, etc. In addition, the geometry can beconsistent with a relatively low or high oscillation harmonic frequency,resulting in a relatively large or small shear penetration depths(δ_(s)=√{square root over (η/pπf)}) into the fluid under concernrespectively. Also, the amplitude of oscillation induced in the physicalelement can be controlled by the current applied through the either oneof the conductors 110 and 111 subsequently controlling the shear rate({dot over (γ)}) applied to the fluid.

FIG. 2(a) shows embodiments of a substrate layer comprising a physicalelement which is suitable for measuring properties of a fluid, inparticular a biological fluid, before and during a chemical reaction. Asshown in FIG. 2(a), there is provided a substrate layer assembly 200 forintegration into a disposable test strip embodiment of the sensor deviceof the invention.

FIG. 2(b) shows an exploded schematic of an assembly for integrationinto a disposable test strip. An substrate layer 201 is patterned toform a rectangular suspended element with 4 meandering compliantstructures, the compliant structures being attached to the suspendedelement at one end and the main body of the substrate layer at theother. The physical element structure may be formed by any appropriatemethod, such as the conventional methods of laser, CNC milling orchemical etching or by stamping of the substrate layer. Independent andisolated patterned conductive tracks 202 and 203 are disposed on thesubstrate layer 201. These conductive tracks may be disposed by anyappropriate method such the conventional methods of as screen printingor inkjet printing and can be composed of any suitably conductive andchemically inert material. A patterned insulating dielectric layer 204is disposed onto the conductive tracks 202 and 203 such that theconductive tracks are completely insulated everywhere except on a region205 and 206 dedicated to providing electrical connections to thephysical element.

FIG. 3 illustrates a further embodiment. FIG. 3(a) shows a furtherembodiment of a sensor device in the form of a disposable test strip300. FIG. 3(b) shows an exploded schematic of the disposable test strip300 of FIG. 3(a). The disposable test strip 300 comprises a basesubstrate 301, onto which is disposed a hydrophilic wicking layer 302,which may optionally comprise a reagent to facilitate a chemicalreaction. The reagent may be present as a sublayer. Alternatively, areagent could be provided upon any internal surface of the chamber. Afirst chamber forming layer 303 is disposed onto the hydrophilic wickinglayer 302. This chamber forming layer may be formed, e.g., using apatterned pre-cast film, or by screening printing or inkjet printing asuitable non-reactive polymeric material. The chamber forming layer ispatterned to have a cut-out 304 to form the chamber wall, in thevicinity of the physical element allowing for it to be suspended forunimpeded motion or oscillation. The assembled “bottom stack” of layerscomprise of the base substrate 301, hydrophilic layer 302 and firstchamber forming layer 303. The reagent layer to facilitate the reactionin the chamber could alternatively be loaded onto the exposed surface ofthe hydrophilic wicking layer 302, after the “bottom stack” of thelayers is assembled. A second chamber forming layer 306 is laminated toa second hydrophilic layer 308 also provided with a reagent layer, ifneeded. The chamber forming layer is patterned to have a similar cut-out307, optionally but not necessarily the same, as in the first chamberforming layer 303 in the vicinity of the physical element allowing forit to be suspended for unimpeded motion or oscillation. A polymeric film309 is then laminated onto the top of the second hydrophilic layer. Thepurpose of film 309 is to provide an upper seal layer on the reactionvessel and to protect the underlying structures of the remainder of thetest strip from mechanical damage. The layers 301, 303 and 306 furtherimproves the stiffness of the disposable test strip. The hydrophiliclayer 308 and the polymeric film 309 are patterned to have a triangular310 and a rectangular 311 opening, to serve as ports for introducingfluid into the strip and a vent to permit air to escape from the chamberas it is loaded with a fluid sample, respectively. The opening size,shape and geometry may be designed and selected to optimize the fluidintroduction and air venting in the chamber.

A physical element sensor device assembly 305, such as that detailed inthe embodiment depicted in FIGS. 2(a) and 2(b) may be laminated over the“bottom stack” comprising the base substrate 301, hydrophilic layer 302and first chamber forming layer 303. The assembled “top stack” oflayers, comprising the second chamber forming layer 306, hydrophiliclayer 308 and the polymeric film 309, is disposed over and laminated onto the physical element sensor device assembly attached to the “bottomstack” of layers, such that the physical element is suspended within a“chamber” as defined by the hydrophilic layers 302 and 308, and theside-walls of the cut-outs 304 and 307 in the two chamber forming layers303 and 306. The distance (D) between the bottom 302 or top 308hydrophilic layers and the physical element sensor device assembly 305as defined by the height of the two chamber forming layers 303 and 306,and the geometry of the cut-outs 304 and 307 in the chamber forminglayers can be designed and selected to optimize the volume of thechamber, and optimize the fluid introduction and air venting in thechamber. The distance D or the height of the two chamber forming layers303 and 306 can be further configured to have the oscillating physicalelement induce a standing shear-wave field in the fluid medium in thechamber, between the bottom 302 or top 308 hydrophilic layers and thephysical element sensor device assembly 305. In order to have aconsistent and reliable standing shear-wave field induced, depending onthe fluid properties the distance D can be configured to be smaller thanor equal to the shear penetration depth (δ_(s)=√{square root over(η/pπf)}). The lower the ratio of the distance D to the shear wavelength(λ_(s)) of the field induced in the medium surrounding the physicalelement, the higher is the consistency and uniformity of the acousticfield set up in the fluid medium, where λ_(s)=2πδ_(s)/√{square root over(2)}cos(δ_(l)/2) where δ_(s) is the shear penetration depth(δ_(s)=√{square root over (η/pπf)}) and δ_(l) si the loss-tangent angleof the medium. The distance D can be configured to be adjustable orpermanently fixed depending on the properties of the fluid under concernintroduced into the chamber, as noted above. The chamber forming layers303 and 306 can be formed of single or multiple laminated polymericsubstrates to tailor the distance D and, incorporated with pressuresensitive adhesives on both sides to facilitate the lamination to thephysical element sensor device assembly 305 and the hydrophilic layers302 and 308. The acoustic field setup in the fluid trapped between thephysical element and the chamber walls can be used to not only determinethe viscosity of the fluid but also its viscoelastic properties. Also,the presence of the fixed chamber walls close to the oscillatingphysical element offers additional benefits for high accuracy monitoringof the physical properties of the fluid as a function of time.

The structure and arrangement of the elements of the first and/or secondchamber forming layer 303 and 306 may comprise two or more subsidiary,discrete pads arranged in relation to the main body of the chamberforming layers 303 and 306 in order to define an opening which allows asample of fluid to be loaded into the chamber, which is defined by aninternal volume provided within the sensor device. The fluid may be abiological fluid, for example blood. The arrangement of the two or moresubsidiary pads which contribute to the first and/or second chamberforming layer 303 and 306, may be arranged in relation to the main bodyof the first and/or second chamber forming layer 303 and 306 in order tofurther provide at least one further channel or opening, typicallyprovided at a different side of the chamber to the main opening, thesesecondary openings allowing for the side filling of liquids, or which,due to the opening being communicable with the central chamber, alsopermit air to escape from the chamber as it is loaded with a fluidsample.

FIG. 4 shows in-plane (FIGS. 4(a) and 4(b)) and out-of-plane (FIG. 4(c))oscillations computed using Finite Element Analysis (FEA) simulationsinduced in a physical element sensor device assembly, such as thatdetailed in the embodiment depicted in FIGS. 2(a) and 2(b), assembled inthe form of a disposable test strip such as that detailed in theembodiment depicted in FIGS. 3(a) and 3(b). FIGS. 4(a) and 4(b) show thefundamental resonance of in-plane oscillations in the physical elementin the direction of x-axis and y-axis respectively, which can be inducedby fixing the direction of the magnetic field and varying the directionof the applied current or electric field applied to the physical elementor, by varying the direction of the magnetic field and fixing thedirection of the applied current or electric field applied to thephysical element. FIG. 4(c) shows the fundamental resonance ofout-of-plane oscillation in the physical element in the direction ofz-axis, which can be induced by fixing the direction of the magneticfield and varying the direction of the applied current or electric fieldapplied to the physical element or, by varying the direction of themagnetic field and fixing the direction of the applied current orelectric field applied to the physical element. In an embodiment, thein-plane (FIGS. 4(a) and 4(b)) and out-of-plane (FIG. 4(c)) oscillationscould be induced in a single or a combination of multiple physicalelements, in a single or multiple individual chambers.

FIG. 5 through FIG. 8 are discussed in the Examples section below.

FIG. 9 illustrates an embodiment of a meter for interfacing with adisposable strip device according to the invention, such as thatdetailed in the embodiment depicted in FIGS. 3(a) and 3(b). FIGS. 9(a)and 9(b) show an embodiment of the top and bottom halves of the meter,housing a touch-screen display incorporated with a graphical userinterface, electronic circuit boards and battery, which when assembledin a “clam-shell” based arrangement forms a solitary unit forinterfacing with a disposable strip 300 to perform automated measurementof fluid properties. The top and bottom halves of the meter can befabricated using standard techniques including but not limited toStereolithography (SLA), injection molding, 3D printing, CNC milling,etc.

In the meter's top half embodiment (FIG. 9(a)), a logo by name INReady902 is formed on the meter using Stereolithography. An opening 901 forthe display on the meter is provided on the top half of the meter, whichis provided with a touch-screen allowing for user interaction with themeter. A strip-enclosure 903 is provided on the top half to allow forthe insertion of the disposable strip, and an electrical connectorinstalled in the enclosure allows for electrical connectivity betweenthe meter and the strip. A magnet-enclosure 905 is provided to hold amagnet providing a magnetic field, with the field lines intersecting thestrip resting on a substrate 904 when inserted in the enclosure 903.

In the meter's bottom half embodiment (FIG. 9(b)) is provided with twocompartments 908 and 913, which provide an enclosure for the electronics& display, and battery & power switch respectively. The compartment 908holds the electronic circuit board with a display stacked on top, withalignment posts 909 to fix the position of the display with respect tothe top and bottom halves of the meter. The compartment 913 encloses alithium-ion, rechargeable battery that is used to power the electroniccircuit board and display modules. Electronic access ports 915 and 914are provided on the bottom half chassis for charging the battery andelectronic connection to a computer for data access and retrievalrespectively. A recess 916 is provided on the side of the bottom halfchassis for installing a power button to switch the meter ON and OFF.

After installing the necessary components inside the bottom and tophalves of the meter, the meter is assembled by aligning and insertingthe fastening posts such as 907 provided on the top half of the meter,in to the recesses such as 911 provided on the bottom half of the meter.Further tapped through holes are provided through the fastening posts907 and recesses 911 to allow for fastening the top and bottomstructures together to form a solitary unit. Further, thestrip-enclosure 903, substrate 904 and magnet-enclosure 905 align with afillet 910 that is provided for ease of insertion of strip into themeter. In use, the disposable test strip would be inserted into themeter, such as that detailed in the embodiment depicted in FIGS. 9(a)and 9(b), so that the contacts provided at the end of the test stripdevice (205 and 206 shown in FIG. 2) opposite to the chamber, wouldprovide direct electrical connection to the conductive pathways 202 and203 through the physical element.

FIG. 10 shows the process flow of inserting a disposable test strip,such as that detailed in the embodiment depicted in FIGS. 3(a) and 3(b),into the meter to perform measurement on a fluid sample. In FIG. 10(a)the meter prompts the user to insert the strip into the enclosure. Whenthe strip is inserted, the meter performs a calibration on the strip inpreparation for measurement and prompts the user to insert blood asshown in FIG. 10(b). A small sample of biological fluid may be providedeither directly from a wound site, or alternatively the biological fluidmay be provided from a storage container or from an intermediate devicesuch as a dropper which facilitates loading of the fluid into thechamber. Alternatively, the meter can be programmed to accept andanalyze any fluid sample. In FIG. 10(c) the user uses a standard lancingdevice with a 21 gauge needle to supply a drop of blood to be introducedinto the chamber in the strip. A drop of fluid, in this case blood, whenapplied to the opening channel allows the fluid to enter into the mainchamber 310 as seen in FIG. 10(d). Ingress of the fluid into the chamberthrough the opening is typically facilitated by a capillary action, thiscapillary effect resulting from the dimensions and arrangement of thechannel. Other factors, such as the materials used in the constructionof the sensor device may facilitate movement of the fluid into thechamber by capillary motion. As the fluid is drawn into the chamber, theair trapped in the chamber is allowed to vent out through therectangular opening 311.

As blood is drawn into the chamber, the change in the fluid propertiesof the regions around the oscillating physical element results inchanges in the oscillation characteristics of the structure, thisincluding the electronics commencing analysis of the biological fluidsample. During a known time period, the analysis is completed and thechange in viscosity, viscoelasticity and density of the fluid samplebefore, during and after the reaction is measured. After a suitablereaction time has passed, an algorithm would be used to convert thenatural frequency signal and the quality factor measured into a usabletest result.

EXAMPLES

The following specific examples are to be construed as merelyillustrative, and not limitative of the remainder of the disclosure inany way whatsoever. Without further elaboration, it is believed that oneskilled in the art can, based on the description herein, utilize thepresent invention to its fullest extent.

Example 1 Determining the Fluid Characteristics of Ethylene GlycolAqueous Solutions using a Physical Element Sensor Device Assembly

Materials and Methods:

The physical element used in this example was fabricated by lasermachining 3 mil stainless steel 316 sheets to define the suspendedelement and compliant structures essentially as shown in FIG. 2(a). Thesuspended element was fabricated in the shape of a rectangle with alength of 5 mm and width of 2 mm. Four compliant structures werefabricated in a meandering shape with a width of 0.125 mm and a totallength of 5.526 mm. A fixture was made to clamp the other ends of thefour compliant structures attached to the suspended element, and toprovide electrical connectivity through the suspended element. Thefixture was designed to have a chamber into which the physical elementwas suspended, which had fluidic ports to flow the liquid under concernthrough the chamber. A low-noise pre-amplifier (Stanford Research SR560)and a DSP lock-in amplifier (Stanford Research SR850) was used to applythe current through the suspended element and measure the “detectionvoltage” respectively. Two permanent magnets (sintered, N52 grade,0.1-0.5 T) with radial and axial magnetic poling were used to providemagnetic field in parallel and perpendicular to the suspended elementrespectively. An enclosure was provided in the fixture which enabledfixing the relative position of the physical element and the magnet.Ethylene glycol solutions were prepared using de-ionized water invarying concentration ranging from 0 to 100% as shown in Table I. Thesolutions were prepared in 20 ml de-ionized water and correspondingvolume of ethylene glycol solutions concentrations.

The solutions were introduced into the chamber so that the physicalelement was completely immersed and was then analyzed to ensure thatthere were no air bubbles present in the chamber. Current on the orderof 10 mA at varying frequencies (detailed in the results section below)was introduced into the physical element via a first set of suspendedelements along the short edge of the rectangular suspended element inthe presence of a magnetic field in the range of 0.1 to 0.5 T dependingon the distance from the surface of the magnet. When the magnetic fieldwas applied perpendicular to the physical element, in-plane motion alongthe long edge of the rectangular suspended element (as seen in FIG. 4A)corresponding to the fundamental frequency of resonance was induced.When the magnetic field was applied parallel to the physical element,out-of-plane motion in a direction perpendicular to the rectangularsuspended element (as seen in FIG. 4C) corresponding to the fundamentalfrequency of resonance was induced. The oscillation characteristics ofthe physical element viz. amplitude, frequency and quality factor weremeasured by measuring the “detection voltage” induced viaelectromagnetic induction at varying frequencies, along the second setof suspended elements along the short edge of the rectangular suspendedelement (on the opposite side as the first set). The quality factor wascomputed by the ratio of the measured resonance frequency to the widthof the resonance peak as measured by the full width half max (detailedexplanation provided in the definitions).

TABLE I Ethylene Glycol (v/v) [%] Viscosity (cP) Density (gm/cc) 01.0021 0.99822 3.12 1.2789 1.01093 4.87 1.4602 1.0177 6.77 1.64651.02452 10 1.9903 1.03508 16.22 2.7938 1.05178 20 3.3431 1.06 22.5 3.7111.06479 30.03 4.9174 1.07657 40.38 6.8247 1.08806 53.73 9.6558 1.0978472.32 13.7082 1.10616 100 20.8064 1.11323

Results:

Performance of Sensor in Air:

An example of a frequency scan in air for in-plane and out-of-planeoscillation of the physical element is shown in FIGS. 5(a) and 5(b)respectively. The frequency sweep for the in-plane and out-of-planeoscillations were performed in the ranges of 4100 to 4550 Hz, and 400 to800 Hz to measure a resonance frequency of 4495 Hz and 700 Hzrespectively.

Liquid Sensing Characteristics

The raw data from the frequency scans of the in-plane and out-of-planemodes of the physical element when immersed in ethylene glycol aqueoussolutions of 0, 10, 20 and 30% is shown in FIGS. 6(a) and 6(b)respectively. Increasing concentrations of ethylene glycol dampen thesensor, such that the amplitude and frequency decreases. As thesolutions become denser and more viscous it causes the physical elementto oscillate more slowly through the liquid for both in-plane andout-of-plane modes, and correspondingly the frequency decreases.

The analysis of the frequency scans from the in-plane mode of thephysical element when immersed in varying concentrations of ethyleneglycol is shown in FIG. 7. FIGS. 7(a) and 7(c) shows a linearrelationship between the amplitude and quality factor, and the inversesquare-root of the product of density and viscosity (1/√{square rootover (ηp)}) of the ethylene glycol solutions. FIG. 7(b) shows apolynomial relationship between the in-plane resonance frequency and theinverse square-root of the product of density and viscosity (1/√{squareroot over (ηp)}) of the ethylene glycol solutions.

The analysis of the frequency scans from the out-of-plane mode of thephysical element when immersed in varying concentrations of ethyleneglycol is shown in FIG. 8. FIG. 8(a) shows a linear relationship betweenthe amplitude and the density of the ethylene glycol solutions, and FIG.8(b) shows a polynomial relationship between the out-of-plane resonancefrequency and the density of the solutions.

By monitoring the in-plane and out-of-plane oscillations of the physicalelement, the viscosity and density of an arbitrary fluid can be deduced.The density of a fluid can be estimated from the out-of-plane modecharacteristics and the viscosity-density product can be estimated fromthe in-plane mode, thus allowing for the independent and absolutemeasurement of density and viscosity of the fluid under concern. Thesensor exhibited linearity in measuring the viscosity and density in therange of 1-20 cP and 0.998-1.113 gm/cc. This linearity enables theaccurate determination of the absolute values of blood viscosity anddensity with typical ranges of 5-20 cP and 1.032-1.080 gm/ccrespectively. In addition, since the density is linearly related to thehematocrit in a blood sample by the simple relationship p=1.026+0.067Hct gm/cc hematocrit can be accurately ascertained from themeasured blood density, since the device operation was demonstrated tobe linear in that range as shown in FIG. 8.

Example 2 Determining of the INR and TEG of Human Blood using a PhysicalElement Sensor Device Assembly

Materials and Methods:

FIG. 3(b) shows an exploded schematic of the disposable test strip 300of FIG. 3(a).The strip was fabricated and assembled using standarddiagnostic test strip manufacturing materials made of polyester-basedsubstrates with acrylic adhesives to hold the structure in place.

Strip Bottom Stack Assembly:

The base substrate 301 was composed of 2 layers of a single-sidedpressure sensitive adhesive (PSA) with a total thickness of 0.0124″(8259, Adhesives Research, Inc.) to provide structural support. Apolyester substrate with a hydrophilic wicking layer on one side 302with a thickness of 0.0045″ (ARFlow 90469, Adhesives Research, Inc.) waslaminated onto the base substrate, with the hydrophilic side facing awayfrom the base substrate. A first chamber forming layer 303, composed ofa double-sided PSA with a thickness of 0.0034″ (9965, 3M, Inc.), waspatterned to have a cut-out 304 to form the chamber wall in the vicinityof the physical element. The assembled “bottom stack”, comprising of thebase substrate 301, hydrophilic layer 302 and the first chamber forminglayer 303, was patterned to form the foot-print of the strip (1.6×2.5cm²) surrounding the chamber as shown in FIG. 3. The reagent layer tofacilitate the reaction in the chamber could alternatively be loadedonto the exposed surface of the hydrophilic wicking layer 302, after the“bottom stack” of the layers is assembled.

Strip Top Stack Assembly:

A second chamber forming layer 306 fabricated in the same manner as thefirst chamber forming layer was laminated to a second hydrophilic layer308. The chamber forming layer was patterned to have a similar cut-out304 as in the first chamber forming layer 303. A clear polyester film309 (CG3300, 3M, Inc.), with a printed graphic consisting of the companylogo and location of blood drop introduction, was then laminated ontothe top of the second hydrophilic layer on the side not containing thehydrophilic layer. The purpose of film 309 was to provide an upper seallayer on the chamber and to protect the underlying structures of theremainder of the test strip from mechanical damage. The hydrophiliclayer 308 and the polymeric film 309 were patterned to have a triangular310 and a rectangular 311 opening, to serve as ports for introducingfluid into the strip and to vent to permit air to escape from thechamber as it was loaded with a fluid sample, respectively. Theassembled “top stack”, comprising of the second chamber forming layer306, hydrophilic layer 308 and the polymeric film 309, was patterned toform the foot-print of the strip (1.6×2.5 cm²) surrounding the chamberas shown in FIG. 3.

Physical Element Fabrication:

A physical element sensor device was made by screen printingsilver-based conductive ink on a 0.003″ clear polyester substrate topattern the electrically conductive paths through the physical elementand provide electrical pads to connect to the meter. The physicalelement comprised of the suspended element and compliant structures werepatterned by laser machining the polyester substrate with the conductiveink. The suspended element was fabricated in the shape of a rectanglewith a length of 5 mm and width of 2 mm. Four compliant structures werefabricated in a meandering shape with a width of 0.125 mm and a totallength of 5.526 mm.

Prothrombin Time Reagent Incorporation:

The physical element sensor device, assembled “bottom stack” and “topstack” of the strip were incorporated with a reagent comprising ofrabbit brain thromboplastin (Pacific Hemostasis Prothrombin Timereagent, Thromboplastin-DS, Product# 29-227-3), calcium chloride (25 mM)and Tween (2% v/v aqueous solution). The reagent was incorporated bydropping the solution with a pipette on to the exposed hydrophiliclayers in the top and bottom stacks of the strip (10 μl each) and, onthe top and bottom of the physical element sensor device assembly 305(10 μl each), followed by air drying for >7 hours at standard roomtemperature and relative humidity. The ratio of the volume of thereagent to blood that could be contained in the chamber was maintainedat 2:1, with 30 μl of reagent and 15 μl of blood.

Strip Assembly:

The physical element sensor device was laminated over the bottom stackloaded with reagent. The assembled top stack was disposed over andlaminated on top of the physical element sensor device assembly attachedto the bottom stack of layers, such that the physical element wassuspended within a chamber as defined by the hydrophilic layers 302 and308, and the side-walls of the cut-outs 304 and 307 in the two chamberforming layers 303 and 306. The distance (D) between the bottom 302 ortop 308 hydrophilic layers and the physical element sensor deviceassembly 305 as defined by the height of the two chamber forming layers303 and 306 (0.01″), and the geometry of the cut-outs 304 and 307 in thechamber forming layers, were selected to have a total blood volumecontained by the chamber to be 15 μl. The blood wicked into the chamberwhen it was introduced into the triangular opening 310, and displacedthe air in the chamber through the rectangular opening 311.

The meter used to perform the measurement was fabricated using standardsteriolithography SLA processes with a design as shown in FIG. 9. Acustom printed circuit board with a microcontroller was provided in themeter to actuate the physical element sensor device embedded in thestrip by injecting/applying time-varying currents through the conductivepaths at oscillation frequencies in the vicinity of the resonancefrequency of the physical element. The meter was provided with astandard resistive touch-screen display with a graphical user interfaceto interact with the instrument for example to start the measurement,and to display the results in real-time as shown in FIG. 10.

Results:

Blood coagulation tests were performed using the strip and meterfollowing the workflow detailed in FIG. 10 as previously described. Whenblood was introduced into the chamber of the strip as per the workflowdetailed in FIG. 10, coagulation was induced as the blood flowed intothe chamber and mixed with the dried reagent incorporated in thechamber. Before and during blood coagulation, the absolute bloodviscosity was measured instantaneously using the in-plane oscillationcharacteristics of the physical element and was plotted on the meterdisplay as shown in FIG. 11. The Prothrombin Time (PT) of the blood wascalculated based on the rate of increase in blood viscosity as afunction of time 111, and the deduced International Normalized Ratio(INR) was displayed on the screen in less than 30 seconds as shown inFIG. 11(a). After the blood clot was formed, the measurement of in-planevibration was continued and the viscoelastic properties of the bloodclot formed between the physical element sensor device assembly and thehydrophilic layers in the chamber was determined. The bloodviscoelasticity was plotted on the screen as shown in FIG. 11(b), whichcould be representative of a standard blood test known as thethromboelastograph (TEG) 112. The amplitudes of the blood viscosity 111and viscoelasticity 112 as plotted on the screen were shown in arbitraryvalues to represent the fluid property variation trend/profile as theblood clots. This demonstrates the capability of the meter and strip toperform multiple blood coagulation tests on the same blood sample.

Listing of Features and Embodiments

The following list provides additional features that may be present indevices and/or methods according to the invention.

-   -   1. The substrate layer may be composed of a material which is        selected from a group of materials including polymers such as        polyester (PET), plastics, printed circuit board, etc., and/or        may be fabricated using mass manufacturing methods including        roll-to-roll continuous flow manufacturing.    -   2. The suspended element and compliant structures of the        substrate layer may be patterned/formed by a technique selected        from etching, laser treatment, printing and mechanical        punching/cutting.    -   3. An electrically conductive path running across compliant        structures and a suspended element may comprise pure metals        (Silver, Gold, Palladium, Titanium, Tungsten, Platinum,        Stainless Steel, etc.), metal alloys, conductive polymers, etc,        and/or the electrical path may be incorporated on top, bottom,        inside or as part of the active substrate.    -   4. An electrically conductive path running across compliant        structures and a suspended element may be formed by a technique        selected from metal evaporation, thin metal film extrusion,        printing or laser treatment.    -   5. When actuating oscillation of and measuring signal from a        suspended element, an electrical field can be applied and a        detection signal can be measured across independent electrically        conductive pathways.    -   6. When actuating oscillation of and measuring signal from a        suspended element, vibration can be induced through a        time-varying electrical field and constant magnetic field, or a        constant electrical field and time-varying magnetic field. The        time-varying field may correspond to at least one of the        suspended element's fundamental or harmonic frequencies of        vibration.    -   7. The detection signal resulting from oscillation of the        suspended element monitored in a range of frequencies in the        vicinity (e.g., within a factor of 1.5, 2, 3, 4 or 5) of the        frequency of the time-varying excitation field or fields.    -   8. Oscillation of a suspended element or of two or more        independent suspended elements may be induced at two or more        frequencies, and the oscillations may comprise two in-plane        oscillations at different frequencies and/or an in-plane        oscillation and an out-of-plane oscillation.    -   9. The upper and lower layers of a device according to the        invention can be positioned at a fixed or adjustable distance        above and below the substrate layer, and/or the substrate layer        can be clamped or affixed to the upper and lower substrates        everywhere except the suspended element(s) and attached        compliant structures.    -   10. Methods according to the invention can comprise inducing a        standing shear-wave field in the medium between a suspended        element and one or both of the upper and lower layers.    -   11. Devices according to the invention may comprise additional        layers such as those shown in FIG. 3(b).    -   12. One or more layers of a device according to the invention        may comprise at least one channel or opening suitable to permit        the entry of a fluid sample into the reaction chamber, which        optionally may be of suitable dimensions such that the fluid        sample can enter into said reaction chamber by means of        capillary action, and/or at least one channel or opening        suitable to permit the displacement of air therethrough upon the        filling of the reaction chamber with a fluid sample.    -   13. At least one surface of the chamber of a device may have a        low contact angle with fluids (e.g., less than or equal to 45        degrees), which can facilitate substantially full occupancy of        the chamber by an aqueous fluid sample.    -   14. Methods may comprise computing static or dynamic        viscoelastic properties of a fluid from the measured viscosities        and/or density of fluid at different applied shear rates ({dot        over (γ)}); theoretical or empirical models may be used in such        computations.    -   15. A change in one or a combination of oscillation        characteristics of at least one suspended element may be used in        methods to determine the fluid properties before, during and/or        after a chemical reaction in the sample.    -   16. Methods in which a blood sample is analyzed may comprise        bringing a blood sample into contact with at least one blood        clotting agent before, during or after introduction of the        sample into a chamber, wherein the oscillation characteristics        of at least one suspended element are used to determine blood        fluid properties and blood clotting reaction dynamics such as        clotting time in PT, PTT, and/or ACT coagulation tests.    -   17. Methods in which a blood sample is analyzed may comprise        determining the concentration of red blood cells or hematocrit        in the blood sample. This determination may be performed or may        use data acquired prior to bringing the fluid into contact with        a clotting reagent. Blood clotting reaction dynamics and/or        blood fluid properties may be calibrated or adjusted using the        measured hematocrit.    -   18. When analyzing a blood sample comprising an anticoagulant,        methods may comprise determining the concentration of        anticoagulant in the blood sample.    -   This may be performed or may use data acquired prior to bringing        the blood sample into contact with the clotting reagent.

The following list provides additional non-limiting examples of systemsand methods contemplated according to the invention.

1. A system for measuring a fluid, comprising:

-   -   a fluidic resonator configured to apply a shear rate and stress        to the fluid;    -   a sensor configured to measure a vibration of the fluidic        resonator during application of the applied shear rate and        stress; and    -   a processor configured to identify a parameter indicative of a        viscosity and/or density of the fluid based on a damping of the        vibration of the resonator caused by the fluid at a fixed        applied shear rate/stress.

2. The system of embodiment 1, wherein the sensor is configured tomeasure at least one of (a) a quality factor of the vibration, (b) aresonance frequency of the vibration, (c) an amplitude of the vibration,and (d) a phase of the vibration.

3. The system of embodiment 1, wherein the sensor is configured tomeasure a combination of (a) a quality factor of the vibration, (b) aresonance frequency of the vibration, (c) an amplitude of the vibration,and (d) a phase of the vibration.

4. The system of embodiment 1, wherein the resonator is a purelyin-plane resonator.

5. The system of embodiment 1, wherein the resonator is a purelyout-of-plane resonator.

6. The system of embodiment 1, further comprising:

-   -   a thermal sensor configured to sense a temperature of the fluid        during the measurement of the vibration; and    -   a thermal actuator configured to control a temperature of the        fluid during the measurement of the vibration.

7. A method of measuring a fluid, comprising:

-   -   applying a shear rate and stress to the fluid via a fluidic        resonator;    -   measuring a vibration of the fluidic resonator during the        application of the applied shear rate and stress; and    -   identifying a parameter indicative of a viscosity and/or density        of the fluid based on a damping of the vibration of the        resonator caused by the fluid, at a fixed applied shear        rate/stress.

8. The method of embodiment 7, wherein:

-   -   the measured vibration is an in-plane vibration of the fluidic        resonator at a frequency fat a fixed applied shear rate/stress        such that the penetration depth of the shear wave        (δ=Sqrt(η/pπf)) is relatively small; and    -   the identified parameter is indicative of the viscosity of the        constant phase (η_(cp)) of a complex non-Newtonian fluid.

9. The method of embodiment 7, wherein:

-   -   the measured vibration is an in-plane vibration of the fluidic        resonator at a frequency fat a fixed applied shear rate/stress        such that the penetration depth of the shear wave        (δ=Sqrt(η/pπf)) is relatively large, and    -   the identified parameter is indicative of the viscosity of the        bulk (η_(bulk)) of a complex non-Newtonian fluid.

10. The method of embodiment 7, wherein the identified parameter isindicative of a concentration of an additive (c_(s)) in a non-Newtonianfluid,

11. The method of embodiment 10, wherein the non-Newtonian fluidincludes particulates or solid-phase objects.

12. The method of embodiment 7, further comprising:

-   -   identifying a standardized measure of bulk viscosity of a        complex non-Newtonian fluid at a standardized additive        concentration as a function of the fluid's properties.

13. The method of embodiment 12, wherein the standardized measure isidentified as a function of one or more of viscosity of constant phaseof fluid (η_(cp)), viscosity of bulk of fluid (η_(bulk)) andconcentration of additive (c_(s)).

14. The method of embodiment 7, further comprising:

-   -   computing static or dynamic,as a function of time, viscoelastic        properties of a complex non-Newtonian fluid from the measured        viscosities and/or densities of fluid at different applied shear        rates ({dot over (γ)}) using different theoretical or empirical        models.

15. The method of embodiment 14, wherein the viscoelastic propertiesinclude yield stress (τ_(y)).

16. The method of embodiment 14, wherein the viscoelastic properties aredetermined according to Casson's model—

$\eta_{bulk} = {\frac{\left( {\sqrt{\tau_{y}} + \sqrt{k\; \overset{\circ}{\gamma}}} \right)^{2}}{\overset{\circ}{\gamma}}.}$

17. The method of embodiment 7, further comprising:

computing static or dynamic viscoelastic properties of a complexnon-Newtonian fluid, from the standardized bulk viscosities of fluidcomputed at different concentrations of additive (c_(s)) and appliedshear rates ({dot over (γ)}) using different theoretical or empiricalmodels , thereby allowing for identification of an empiricalrelationship between the fluid property and concentration of additive(c_(s)).

18. The method of embodiment 17, wherein the viscoelastic propertiesinclude yield stress (τ_(y)).

19. The method of embodiment 17, wherein the viscoelastic properties aredetermined according to Casson's model—

$\eta_{bulk} = {\frac{\left( {\sqrt{\tau_{y}} + \sqrt{k\; \overset{\circ}{\gamma}}} \right)^{2}}{\overset{\circ}{\gamma}}.}$

LIST OF REFERENCES CITED

-   1. G. D. O. Lowe, “Blood rheology in arterial disease,” Clinical    Science, vol. 71, pp. 137-146, 1986.-   2. G. D. O. Lowe, “Blood rheology and vascular disease,”    Haemostatsis and Thrombosis (ed. by A. L. Bloom et al), 3^(rd) edn,    pp. 1169-1188. Churchill Livingstone, Edinburgh, 1994.-   3. L. Dintenfass, “Blood Microrheology: viscosity factors in blood    flow ischaemia and thrombosis,” Butterworth, London, 1971.-   4. G. D. O. Lowe, W. C. S Smith, H. D. Tunstall-Pedoe, I . K.    Crombie, S. E. Lennie, J. Anderson, J. C. Barbenel, “Cardiovascular    risk and haemorheology: results from the Scottish Heart Health Study    and the MONICA project, Glasgow,” Clinical Haemorheology, vol. 8,    pp. 518-524, 1988.-   5. G. D. O. Lowe, A. J. Lee, A. Rumley, J. F. Price, F. G. R.    Fowkes, “Blood viscosity and risk of cardiovascular events: the    Edinburgh Artery Study,” British Journal of Haematology, vol. 96,    pp. 168-73, 1997.-   6. G. Ciuffetti, G. Schillaci, R. Lombardini, M. Pirro, G. Vaudo, E.    Mannarino, “Prognostic impact of low-shear whole blood viscosity in    hypertensive men,” European Journal of Clinical Invesigation, vol.    35 no. 2, pp. 93-98, February 2005.-   7. R. Rosencranz, S. A. Bogen, “Clinical laboratory measurement of    serum, plasma, and blood viscosity,” American Journal of Clinical    Pathology, vol. 125, Suppl. 1, pp. S78-S86, 2006.-   8. A. Matrai, R. B. Whittington, E. Ernst, “A simple method of    estimating whole blood viscosity at standardized hematocrit,”    Clinical Haemorheology, vol. 7, pp. 261-265, 1987.-   9. W. I. Rosenblum, “In vitro measurements of the effects of    anticoagulants on the flow properties of blood: The relationship of    these effects to red cell shrinkage,” Blood, vol. 31, no. 2, pp.    234-241, 1968.-   10. E. Nwanko, C. J. Durning, “Fluid property investigation by    impedance characterization of quartz crystal resonators (2 parts),”    Sensors and Actuators A. Physical, vol. 72, pp. 99-109, 1999.-   11. B. Jakoby, M. Scherer, M. Buskies, H. Eisenschmid, “An    automotive engine oil viscosity sensor,” IEEE Sensors Journal, vol.    3, pp. 562-568, 2003.-   12. S. Chien, J. Dormandy, E. Ernst, A. Matrai, “Clinical    Hemorheology,” Martinus Nijhoff Publishers, Dordrecht, 1987.-   13. J. Wang, “Electrochemical Glucose Biosensors,” Chemical Reviews,    vol. 108, pp. 814-825, 2008.

The specification is most thoroughly understood in light of theteachings of the references cited within the specification. Theembodiments within the specification provide an illustration ofembodiments of the invention and should not be construed to limit thescope of the invention. The skilled artisan readily recognizes that manyother embodiments are encompassed by the invention. All publications andpatents cited in this disclosure are incorporated by reference in theirentirety. To the extent the material incorporated by referencecontradicts or is inconsistent with this specification, thespecification will supersede any such material. The citation of anyreferences herein is not an admission that such references are prior artto the present invention.

Unless otherwise indicated, all numbers expressing quantities ofingredients, reaction conditions, and so forth used in thespecification, including claims, are to be understood as approximationsand may vary depending upon the desired properties sought to be obtainedby the present invention. At the very least, and not as an attempt tolimit the application of the doctrine of equivalents to the scope of theclaims, each numerical parameter should be construed in light of thenumber of significant digits and ordinary rounding approaches. Therecitation of series of numbers with differing amounts of significantdigits in the specification is not to be construed as implying thatnumbers with fewer significant digits given have the same precision asnumbers with more significant digits given.

The use of the word “a” or “an” when used in conjunction with the term“comprising” in the claims and/or the specification may mean “one,” butit is also consistent with the meaning of “one or more,” “at least one,”and “one or more than one.” The use of the term “or” in the claims isused to mean “and/or” unless explicitly indicated to refer toalternatives only or the alternatives are mutually exclusive, althoughthe disclosure supports a definition that refers to only alternativesand “and/or.”

Unless otherwise indicated, the term “at least” preceding a series ofelements is to be understood to refer to every element in the series.Those skilled in the art will recognize, or be able to ascertain usingno more than routine experimentation, many equivalents to the specificembodiments of the invention described herein. Such equivalents areintended to be encompassed by the following claims.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although any methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of the present invention, the preferred methodsand materials are now described.

The publications discussed herein are provided solely for theirdisclosure prior to the filing date of the present application. Nothingherein is to be construed as an admission that the present invention isnot entitled to antedate such publication by virtue of prior invention.Further, the dates of publication provided may be different from theactual publication dates which may need to be independently confirmed.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

1-8. (canceled)
 9. A method of determining one or more properties orchanges in properties of a fluid sample, the method comprising: placingthe fluid sample in a chamber comprising a physical element capable ofoscillating, the oscillation being one of in-plane, out-of-plane, orcombinations thereof; oscillating the physical element at one or moreoscillation frequencies; inducing at least one acoustic field in thefluid sample; measuring one or more characteristics of one or moreoscillations of the physical element; and determining one or moreproperties or changes in properties of the fluid sample using one ormore of the measured oscillation characteristics.
 10. The method ofclaim 1, wherein the measured oscillation characteristic is chosen fromamplitude, phase, frequency, quality factor, and combinations thereof.11. The method of claim 1, wherein the property of the fluid sample ischosen from viscosity, viscoelasticity, density, and combinationsthereof.
 12. The method of claim 1, wherein the fluid sample iscomprised of one or more analytes.
 13. The method of claim 6, wherein atleast one of the acoustic fields has a penetration depth greater thanthe size of at least one analyte in the fluid sample.
 14. The method ofclaim 6, wherein the analyte is chosen from red blood cells, platelets,fibrinogen, bacteria, and macromolecules or macromolecular complexes.15. The method of claim 6, wherein one or more properties or changes inproperties of at least one analyte in the fluid sample is determined,using one or more of the measured properties or changes in properties ofthe fluid sample and optionally one or more of the measured oscillationcharacteristics of the physical element.
 16. The method of claim 9,wherein the property of the analyte is chosen from size, shape,concentration, mechanical properties, and combinations thereof.